sql: skip autoinc IDs generated inside SQL trigger

Currently, if an INSERT is executed inside SQL trigger and it
results in generated autoincrement identifiers, ones will be
displayed as a result of the statement. This is wrong, since we
are not able to divide IDs obtained into those that belong to the
table mentioned in the statement and those that do not belong to
this table. This has been fixed by adding a new argument to
OP_IdxInsert. In case the argument is not 0, recently generated
identifier is retrieved and saved into the list, which is held in
VDBE itself. Note that from now we don't save autoincremented
value to VDBE right in sequence_next() - this operation is moved
to OP_IdxInsert. So that, VDBE can be removed from struct txn.

For example:
box.execute('CREATE TABLE t1 (i INT PRIMARY KEY AUTOINCREMENT);')
box.execute('CREATE TABLE t2 (i INT PRIMARY KEY AUTOINCREMENT);')
box.execute('CREATE TRIGGER r AFTER INSERT ON t1 FOR EACH ROW '..
            'BEGIN INSERT INTO t2 VALUES (null); END')
box.execute('INSERT INTO t2 VALUES (100);')
box.execute('INSERT INTO t1 VALUES (NULL), (NULL), (NULL);')

Result should be:
---
- autoincrement_ids:
  - 1
  - 2
  - 3
  row_count: 3
...

Closes #4188