[FSDP] Implement local_state_dict and load_local_state_dict (#72469)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/72469
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: 149559985
Test Plan: CI
Reviewed By: rohan-varma
Differential Revision: D33919683
fbshipit-source-id: c9f1b43ce04da7db65c4aebf6ac2c7a0ac5e9de8
(cherry picked from commit 55fd6230c9656fdf30a70dcd8071d094d2e67022)
