[FSDP][Reland] Implement local_state_dict and load_local_state_dict (#73300)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/73300
1. Implement the framework to allow user to choose among `state_dict`, `local_state_dict`, and `sharded_state_dict`.
2. Implement ShardedTensor compatible local_state_dict() and load_local_state_dict().
ghstack-source-id: 149951585
Test Plan: CI
Reviewed By: zhaojuanmao
Differential Revision: D34383925
fbshipit-source-id: a93fd5cdc0ad661823181c47ecd1d462b33d1410
(cherry picked from commit 4828bcc4a0165f4d63a51af792d586cf4305b7a7)
