[ReshardingV3] State

[staffik]

We agreed to use the mapping strategy (design doc).

Implementation plan:

• Initial implementation: [reshardingV3] State ShardUIdMapping - initial implementation #12084
  • Add persistently stored shard_uid mapping.
  • Use the mapping in Store::get() for State column.
  • Prohibit prefix or range iter methods with State column.
• Use the mapping in update operations + add tests: feat(resharding) - Resharding mapping state update #12232
• Handle copy_state_from_store in cold_storage.rs (see comment).
• Handle range iter in load_one_subtree in parallel_loader.rs.
• Integration.
• State clean up (e.g. gc parent state when it is no longer referenced by any child), see Shards garbage collection #11883.
• Profiling (see doc), testing.