C API update - added support for key part sort order.

[TarantoolBot]

Parent doc. issue(s): #3746
Related doc. issue(s): #3747 (Lua API)

Product: Tarantool
Since: master
Root document: https://www.tarantool.io/en/doc/latest/dev_guide/reference_capi/
SME: @ mkostoevr

Details

Looks like the box_key_part_def_t type isn't documented, but
BOX_KEY_PART_DEF_SORT_ORDER bit field was added to its flags
member. The possible values are:

BOX_KEY_PART_DEF_SORT_ORDER_ASC: default sort order.
BOX_KEY_PART_DEF_SORT_ORDER_DESC: reversed sort order.
Requested by @ mkostoevr in tarantool/tarantool@e9b5504.