Added predefined system events: box.status, box.id, box.election and
box.schema.

Closes #6260

@TarantoolBot document
Title: Built-in events for pub/sub

Built-in events are needed, first of all, in order to learn who is the
master, unless it is defined in an application specific way. Knowing who
is the master is necessary to send changes to a correct instance, and
probably make reads of the most actual data if it is important. Also
defined more built-in events for other mutable properties like leader
state change, his election role and election term, schema version change
and instance state.

Built-in events have a special naming schema - their name always starts
with box.. The prefix is reserved for built-in events. Creating new events
with this prefix is banned. Below is a list of all the events + their names
and values:

1. box.id
Description - identification of the instance. Changes are extra rare. Some
values never change or change only once. For example, instance UUID never
changes after the first box.cfg. But is not known before box.cfg is called.
Replicaset UUID is unknown until the instance joins to a replicaset or
bootsa new one, but the events are supposed to start working before that -
right at listen launch. Instance numeric ID is known only after
registration. On anonymous replicas is 0 until they are registered
officially.
Value - {
    MP_STR “id”: MP_UINT; box.info.id,
    MP_STR “instance_uuid”: MP_UUID; box.info.uuid,
    MP_STR “replicaset_uuid”: MP_UUID box.info.cluster.uuid,
}

2. box.status
Description - generic blob about instance status. Its most commonly used
and not frequently changed config options and box.info fields.
Value - {
    MP_STR “is_ro”: MP_BOOL box.info.ro,
    MP_STR “is_ro_cfg”: MP_BOOL box.cfg.read_only,
    MP_STR “status”: MP_STR box.info.status,
}

3. box.election
Description - all the needed parts of box.info.election needed to find who
is the most recent writable leader.
Value - {
    MP_STR “term”: MP_UINT box.info.election.term,
    MP_STR “role”: MP_STR box.info.election.state,
    MP_STR “is_ro”: MP_BOOL box.info.ro,
    MP_STR “leader”: MP_UINT box.info.election.leader,
}

4. box.schema
Description - schema-related data. Currently it is only version.
Value - {
    MP_STR “version”: MP_UINT schema_version,
}

Built-in events can't be override. Meaning, users can't be able to call
box.broadcast(‘box.id’, any_data) etc.

The events are available from the very beginning as not MP_NIL. It's
necessary for supported local subscriptions. Otherwise no way to detect
whether an event is even supported at all by this Tarantool version. If
events are broadcast before box.cfg{}, then the following values will
available:
    box.id = {}
    box.schema = {}
    box.status = {}
    box.election = {}

This way the users will be able to distinguish an event being not supported
at all from box.cfg{} being not called yet. Otherwise they would need to
parse _TARANTOOL version string locally and peer_version in netbox.

Example usage:

 * Client:
   ```lua
   conn = net.box.connect(URI)
   -- Subscribe to updates of key 'box.id'
   w = conn:watch('box.id', function(key, value)
       assert(key == 'box.id')
       -- do something with value
   end)
   -- or to updates of key 'box.status'
   w = conn:watch('box.status', function(key, value)
       assert(key == 'box.status')
       -- do something with value
   end)
   -- or to updates of key 'box.election'
   w = conn:watch('box.election', function(key, value)
       assert(key == 'box.election')
       -- do something with value
   end)
   -- or to updates of key 'box.schema'
   w = conn:watch('box.schema', function(key, value)
       assert(key == 'box.schema')
       -- do something with value
   end)
   -- Unregister the watcher when it's no longer needed.
   w:unregister()
   ```

We use a special, less efficient index vtab if a space can store
compressed tuples. The problem is it isn't enough to look at a space
definition to figure out if there are compressed tuples in the space:
there may be compressed tuples left from before the alter operation that
disabled compression, since we don't rebuild tuples on alter. To update
an index vtab dynamically, we implement some complicated logic, but
it's buggy (results in a test failure in EE). Fixing it requires some
non-trivial effort, because a vtab may be changed after index creation
(when a space format is updated).

Let's drop this optimization altogether for now and use the same vtab
for both compressed and uncompressed indexes. We might return to this
issue in future, but first we need to run some benchmarks to check if
this optimization is worth the complexity. Possible ways how we could
resurrect this optimization:
 - Call get_raw from get directly (without function pointer), inline
   memtx_prepare_result_tuple, and move is_compressed flag to struct
   tuple for better cache locality.
 - Rebuild all tuples on space alter and use a different vtab for
   compressed indexes.

NO_DOC=bug fix
NO_TEST=enterprise
NO_CHANGELOG=unrelased

If tuple compression is enabled, txn_stmt::new_tuple points to
a temporary tuple created by uncompressing a compressed tuple stored
in an index. We must use txn_stmt::rollback_info::new_tuple instead.

NO_DOC=bug fix
NO_TEST=enterprise
NO_CHANGELOG=unreleased

We need it for audit log.

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring

Implement complext foreign keys addition to field foreign keys.
They are quite similar to field foreign keys, the difference is:
* The are set in space options instead of format field definition.
* Several fields may be specified in relation.
* By design field foreign keys are more optimal.

One can set up foreign keys in space options:
box.schema.space.create(.. {.., foreign_key=<foreign_key>})
where foreign_key can be of one of the following forms:
 foreign_key={space=..,field=..}
 foreign_key={<name1>={space=..,field=..}, ..}
where field must be a table with local -> foreing fields mapping:
 field={local_field1=foreign_field1, ..}

NO_DOC=see later commits
NO_CHANGELOG=see later commits

Foreign key is a special type of constraint that makes a relation
between spaces. When declared in some space, each tuple in that
space refers to some tuple in another, foreign space. Reference is
defined in foreign key definition as a correspondence of field of
that spaces, local and remote.

Foreign key preserves that reference between tuples and consists
of two checks:
1. When a tuple is added to space with foreign space constraint,
it must be checked that there is a corresponding tuple in foreign
space, with the same values in fields according to foreign key
definitiion.
2. When a tuple is deleted from space that is a foreign space for
some other space, it must be checked that no tuple references the
deleted one.

This commit introduces field foreign keys that link spaces by
just one field. They are declared in tuple format in one of the
following forms:
 space:format{..,{name=.., foreign_key=<fkey>},..}
 space:format{..,{name=.., foreign_key={<name>=<fkey>}},..}
Where fkey has a form of a table:
 {space=<foreign space id/name>, field=<foreign field id/name>}

NO_DOC=see later commits
NO_CHANGELOG=see later commits

There are cases when we need to be sure that a space by given
id or name is not deleted; and if it is replaced (in space cache),
there's need to track pointer to new space. Like ib constraints:
they must hold a pointer to struct space while it's very hard to
determine whether there'a constraint that points to given space.

Implement space pin/unpin for this purpose. You can pin a space to
declare that the space is require to exist. To have to unpin it
when the space is not needed anymore.

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

I'm going to extend space cache API so it should be separated.
One function went to space.h/c.
No logical changes.

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

The previous commit adds tuple constraint lua functions that check
format of entire tuple. The problem was that in those functions
tuple could be accessed only by field indexes.

Add an ability to use field names too.

NO_DOC=see later commits
NO_CHANGELOG=see later commits

Implement whole tuple constraints in addition to field constraints.
They are quite similar to field constraints, the difference is:
 * The are set in space options instead of format field definition.
 * Entire tuple is passed to check function.
 * By design field constraints are a bit more optimal.

One can set up constraint in space options, with one or several
functions that must be present in _func space:
box.schema.space.create(.. {.. constraint='func1'})
box.schema.space.create(.. {.. constraint={name1='func1'})
box.schema.space.create(.. {.. constraint={name1='f1', name2='f2'})

NO_DOC=see later commits
NO_CHANGELOG=see later commits

tuple_format_new has lots of arguments, all of them necessary
indeed. But a small analysss showed that almost always there are
only two kinds of usage of that function: with lots of zeros as
arguments and lots of values taken from space_def.

Make two versions of tuple_format_new:
simple_tuple_format_new, with all those zeros omitted, and
space_tuple_format_new, that takes space_def as an argument.

NO_DOC=refactoring
NO_CHANGELOG=refactoring

Introduce field constraints - limitaions for particular fields.
Each constraint must refer to a function in _func space. For the
first step we expect lua functions with body there.

Field constraint checks are very close to field type checks, so
it's natural to implement them in tuple formats. On the other hand
tuple formats belong to tuple library, that does not include
functions (func.h/c etc), so constraints are split into two parts:
- a part in tuple library that implements arbitrary constraints
 with pointers to functions that actually check constraints.
- a part in box library which uses the part above, sets particular
 check functions and handles alter etc.

There are two not-so-obvious problems that are solved here:
 - Functions in _func space must be preserved while used by such
 constraints. Func pinning is used for this purpose.
 - During initial recovery constraits are created before _func
 space recovery, so we have to pospone constraint initialization.

One can set up constraint for any field in tuple format with one
or several functions that must be present in _func space:
space:format{name='a', constraint='func1'}
space:format{name='a', constraint={name1='func1'}}
space:format{name='a', constraint={name1='func1', name2='func2'}}

So constraint(s) can be set by one function name or by lua table
with function name values. Each consraints has a name that can be
specified directly (with string key in table) or imlicitly set to
the name of function.

The check function receives two arguments: the checking value and
the name of the constraint. Also the name of the failed constraint
is present in raised exception.

The only way to pass the constraint is to return true from its
function. All other values and exception are treated as failure
(exeptions are also logged).

NO_DOC=see later commits
NO_CHANGELOG=see later commits

Now C port allows to add a tuple or raw msgpack to it.

Add another function that encodes and appends given string.

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

gpr_alloc is a small library that is designed for simplification
of allocation of several objects in one memory block. It could be
anything, but special attention is given to string objects, that
are arrays of chars.

Typical usage consist of two phases: gathering total needed size
of memory block and creation of objects in given block.

NO_DOC=refactoring
NO_CHANGELOG=refactoring

There's several important stages of recovery of database: loading
from snapshot, then loading from WAL(s) and then normal operation.

Introduce a global recovery state that shows this stage.

Note that there's already a recovery state in memtx engine which is
very close but still different to the new introduced state. That
state in memtx is a private property of memtx that internally shows
initialization status of memtx spaces and indexes. Memtx can set the
value for convenience' sake, for example it can jump directly to
MEMTX_OK before snapshot loading in case of force recovert.

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

opt_def is an option parser from msgpack by given scheme.
The scheme consists of set of predefined types that the parser
can handle (something like int, enum, str). The problen is that
those predefined types must be generic, but there are cases when
a specific unusual must be parsed.

This patch introduces OPT_CUSTOM type that uses arbitrary function
callback and can be used for any non-generic option value.

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

There are cases when we need to be sure that a function is not
deleted and/or removed from func cache. For example constraints:
they must hold a pointer to struct func while it's very hard to
determine whether there'a constraint that points to given func.

Implement func pin/unpin for this purpose. You can pin a func to
declare that the func must not be deleted. To have to unpin it
when the func is not needed anymore.

NO_DOC=refactoring
NO_CHANGELOG=refactoring

- Use uint32_t for string length. Actually internally it cannot
take more that INT_MAX length, so uin32_t is enough. This change
makes the hash table a bit more compact.
- Rename mh_strnptr_find_inp -> mh_strnptr_find_str. I beleive it
makes it more understandable.

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

I'm going to extend func cache API so it should be separated.
A couple of comments added.
No logical changes.

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

Fill port with a corrupted data in debug (TRASH it) in order to
detect double port destruction early.

Add a comment for func_call function that describes what states
of ports are expected before and after func_call.

Fix port usage in lua using ffi - allocate a full port structure
instead of a (bit smaller) structure port_c. That makes any port
structure to have fixed determined size which in turn makes safe
to cast and use different port types.

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

There must be a normal code flow: if you want to initialize some
structure you should set members you want to and set with defaults
the rest members. Such a code flow would be durable when some new
members are added to the struct.

Make field_def structure to comply those rules.

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

It seems that is was simply forgotten.

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring

Some non-important fixes that are not related to any issue.

NO_DOC=refactoring
NO_CHANGELOG=refactoring

fselect is designed to make selects results in console better
readable for human eyes. The usage is expected to be rare and
by developers only so there's no performance requirements.

Now the API of fselect is:
s:fselect(<key>, <select+fselect option map>, <fselect option map>)

But sometimes there are cases when only some columns are needed
for analysis, while all other columns consume space on screen.

So make an option in fselect that allows to choose which columns
to output (like some other databases allows).

Add an option 'columns' in fselect options along with other its
options with list of columns (by number or name). Allow lua tables
and comma-separated-strings for that.

If options argument in fselect is string, interpret is as columns
options.

NO_DOC=There's no doc about fselect yet, I'll append these change
to the existing doc ticket
NO_CHANGELOG=minor changes in minor feature

Investigation of GNU libunwind problems on the aarch64-linux-gnu
platform drive us to the conclusion that libunwind-1.2.1 provided by
major distribution packages is broken. Not to mention that its test
suite fails with SEGFAULTs.

Last but not least, some distributions, e.g. CentOS 8 (see #4611) do
not provide a libunwind package.

Hence, bundle libunwind: bundling is enabled by default on all
platforms, except for macOS — a system package can be used if its
version is greater or equal than 1.3.0 (minimal version that does not
seem to be broken on aarch64-linux-gnu).

* Add new submodule: bump it to current master.
* Refactor libunwind package search logic out of compiler.cmake.
* Add CMake script for building bundled libunwind.
* Add CMake script for extracting version of libunwind.
* Re-enable backtrace for all RHEL distributions by default.
* Remove libunwind from static build.

Needed for #4002
Closes #4611

NO_DOC=build system
NO_TEST=build system

Information messages have been moved from the critical logging level
to info to avoid false alarms when reading logs.

NO_DOC=commit does not add any new visible functionality

NO_TEST=testing will require more resources than the result it will bring

Added support to netbox's `stream` and `future` objects using the
__autocomplete metamethod.

Closes #6305
NO_DOC=internal

This patch updates the logic in lua_rl_complete() where __index from
a metatable apparently expected to be a table, not a function. It is
rather simple for a table object, but some of them are userdata, so
an __autocomplete method is introduced to be sure it returns a table
with all names suitable for tabcompletion.

Part of #6305
NO_DOC=internal
NO_CHANGELOG=part of a fix

When the deferred DELETE optimization was introduced, it was enabled for
all Vinyl spaces. Though the optimization  should improve write
performance, at the same time it may result in significant degradation
of reads. Let's disable this optimization by default and add a space
option to enable it.

Closes #4501

@TarantoolBot document
Title: Document defer_deletes space option

The new option is a boolean flag that only makes sense for Vinyl spaces
that have secondary indexes. Setting the flag results in deferring
generation of DELETE statements for secondary indexes till compaction of
the primary index. It should speed up writes, because it eliminates a
lookup in the space for REPLACE and DELETE operations. At the same time,
it may result in degradation of reads from secondary indexes, because it
entails an additional lookup in the primary index per each "phantom"
tuple (a tuple that was deleted in the primary index, but not yet in the
secondary index, and hence should be skipped on read).

Example:

```lua
box.schema.space.create('test', {
    engine = 'vinyl',
    defer_deletes = true,
})
```

If omitted on space creation, this option is set to the value of
`box.cfg.vinyl_defer_deletes`, which is false by default.

Tarantool console quits if you type Ctrl+C.
This patch fixes console behavior on sending SIGINT.
Console discards the current input on typing Ctrl+C
and invites user to the new line.

In daemon mode the process will exit after receiving SIGINT.

Test gh-2717 should be skipped on release build, cause it
uses error injection which is enabled only on debug mode.

Fixes #2717

@TarantoolBot document
Title: Use Ctrl+C to discard the input in console

The signal SIGINT discards the input in console mode.
When tarantool executes with -e flag or runs as a daemon, SIGINT
kills the process and tarantool complains about it in log.

During DDL operations triggers of old space and new created space
are swapped. This leads to crash in case if this swap occurs from
space on_replace triggers. This patch banned all DDL operations
from on_replace triggers.

Closes #6920

@TarantoolBot document
Title: Ban DDL operations from space on_replace triggers

Previously user can set function for space on_replace trigger,
which performs DDL operation. This may leads to tarantool crash,
that's why this patch bans DDL operations from on_replace triggers.
All this operations fails with error: "Space on_replace trigger
does not support DDL operations".

This patch fixes an assertion or segmentation fault when getting the
value of MP_EXT via netbox.

Closes #6766

NO_DOC=Bugfix

netbox_perform_request throws a general ClientError exception on
time-out error: it should throw the more suitable and POSIX-compliant
TimedOut exception which sets errno to ETIMEDOUT.

Closes #6144

NO_DOC=There is no mention of what kind of error is returned on timeout
in the net.box documentation.

There was no zeroing of the number of compressed tuples in the case of
space truncation. Also there was no update of compressed tuples count
in case of using memtx mvcc engine. This patch fix these problems.

Follow up #2695

NO_CHANGELOG=bugfix
NO_DOC=bugfix
NO_TEST=test in ee version

Part of #6773

NO_DOC=Doc-request will be added in another commit.
NO_CHANGELOG=Changelog will be added in another commit.

This patch introduces basic DATETIME support in SQL. After this patch,
it will be allowed to select DATETIME values from spaces, insert them
into spaces, and use them in functions. CAST() from DATETIME to STRING,
SCALAR and ANY is also supported.

Part of #6773

NO_DOC=Doc-request will be added in another commit.
NO_CHANGELOG=Changelog will be added in another commit.

NO_CHANGELOG=feature was not released

Closes #6823

@TarantoolBot document
Title: Document msgpack object iterator take_array method

The new method copies the given number of msgpack values starting from
the iterator cursor position to a new msgpack array object. On success
it returns the new msgpack object and advances the iterator cursor. If
there isn't enough values to decode, it raises a Lua error and leaves
the iterator cursor unchanged.

This function could be implemented in Lua like this:

```lua
function take_array(iter, count)
    local array = {}
    for _ = 1, count do
        table.insert(array, iter:take())
    end
    return msgpack.object(array)
end
```

Usage example:

```lua
local mp = msgpack.object({10, 20, 30, 40})
local it = mp:iterator()
it:decode_array_header()       -- returns 4
it:decode()                    -- returns 10
local mp2 = it:take_array(2)
mp2:decode()                   -- returns {20, 30}
it:decode()                    -- returns 40
```

Normalization was unnecessary in negative interval values
close to 0. This led to extra second in result, like:

```
tarantool> date.now() - date.now()
---
- -1.000026000 seconds
...
```

We do need to normalize when assign to datetime values, but not for
intermediate intervals.

Closes #6882

NO_DOC=bugfix

The problem is memtx_tuple_new() says address of memtx_tuple, while
memtx_tuple_delete() says address of an actual tuple (part of memtx_tuple).
Different addresses in log may be confusing so the patch fixes the problem.

Closes #6634

NO_CHANGELOG=no visible changes
NO_DOC=no visible changes

 - Remove lz4 from link libraries, because it can be linked via
   EXTRA_CORE_LINK_LIBRARIES. It'd be more correct, because the
   open-source doesn't use lz4. Follow-up commit 55f968b4 ("msgpack:
   add stubs for compressed data support").

 - Add OpenSSL include directories unconditionally, because they are
   used in the open-source build since commit e5ec324d ("Move
   OpenSSL initialization to lib/core/ssl").

NO_DOC=cmake
NO_CHANGELOG=cmake