Tracking: Deprecate TableFragments

[shanicky]

After switching to the SQL Backend, we gained native support for point queries of actor/fragment, eliminating the need to retrieve a large PbTableFragments key from etcd and then traverse it hierarchically as before.

However, many compatibility codes from v1 to v2 still use TableFragments, so when we switch to the pure SQL backend implementation of 2.0, we can remove this TableFragments structure.

• Deprecate list_all_table_fragments function. #18095
• Deprecate extract_fragment_and_actors_from_table_fragments and compose_table_fragments function #18096
• TBD