sql: better LUA arguments conversion for UDFs

Start using comprehensive serializer luaL_tofield() to prepare
LUA arguments for UDFs. This allows to support cdata types
returned from Lua function.

Needed for #4387

@TarantoolBot document
Title: UDF returning nil or box.NULL in SQL

Values nil and box.NULL returned by UDF in SQL
both transformed to SQL NULL and are equal.

Example:
tarantool> box.execute("SELECT LUA('return box.NULL') is NULL
                               and LUA('return nil') is NULL")
---
- metadata:
  - name: LUA('return box.NULL') is NULL and LUA('return nil') is NULL
    type: boolean
  rows:
  - [true]
...