`double` field type new behaviour

Related dev. issue(s): https://github.com/tarantool/tarantool/issues/9965
Product: Tarantool
Since: 3.4
Root document:

• https://www.tarantool.io/en/doc/latest/reference/reference_sql/sql_user_guide/#sql-data-type-double
• https://www.tarantool.io/en/doc/latest/platform/ddl_dml/value_store/

SME: @ Gerold103

Details

Double field type now is identical to number. I.e. it can
store integers and compares them as integers.

• Reference -> SQL reference -> SQL user guide:
  DOUBLE values are numerics that do contain decimal points (for
  example 0.5) or are expressed with exponential notation (for
  example 5E-1) -> now DOUBLE can have any numbers, including
  integers. It becomes identical to NUMBER.

• Platform -> Defining and manipulating data -> Data storage:
  the storage type is MP_DOUBLE and the size of the encoded
  value is always 9 bytes. In Lua, fields of the double type
  can only contain non-integer numeric values and cdata values
  with double floating-point numbers -> not so anymore.
  double field is now identical to number (it can store
  integers too, and compares them like integers).

Requested by @ Gerold103 in https://github.com/tarantool/tarantool/commit/60272e8292ad5a893cc14d0318a30f5cfabb6495.

Start with the SQL data type and Data storage root documents linked in the issue. Check each statement about DOUBLE values, storage encoding, and Lua field values against the behavior described here. Done means both pages accurately state that double accepts integers and is identical to number, including integer comparisons.