box: rework box_lua_{call, eval} to use input port

Re-factor box_lua_call and box_lua_eval so that they don't take
call_request. This approach is more scalable: in case of a
functional index, the user expects to see a tuple with field
names so we should be able to pass not only raw msgpack, but
also a tuple to a Lua call so we need an universal way to pass
arguments to _call methods.

To pass a tuple msgpack introduced a new port_msgpack: the port
class with dump_lua method.
A new method get_msgpack returns a content of a port as a
msgpack data. The lifecycle of the returned value is
implementation-specific: it may either be returned directly from
the port, in which case the data will stay alive as long as the
port is alive, or it may be allocated on the fiber()->gc, in
which case the caller is responsible for cleaning up.

Needed for #4182, #1260