New ```index_object.parts``` methods

[AArdeev]

Product: Tarantool
Since: 3.1
Audience/target: who will read it and for what task?
Root document:

• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_index/parts/
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/key_def/

SME: @ locker

Details

index_object.parts has the following methods: validate_key(), validate_full_key(), validate_tuples(), compare_keys().
For their description and usage examples, refer to Module key_def.