[shard] add back init_from_local_shard_and_global_metadata API (#69226)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/69226
This add back the previous init_from_local_shards API, but renamed it to init_from_local_shard_and_global_metadata. It's a partial revert of D32147888 (https://github.com/pytorch/pytorch/commit/35712a8eb4eb9109c4c675ad8b3c249bb539af8d). We now provide two APIs:
1. `init_from_local_shards`: user don't need to provide global metadata and we do all_gather under the hood, the other that
2. `init_from_local_shards_and_global_metadata`: user need to explicitly construct ShardedTensorMetadata to use this API, need to ensure correctness on all ranks, as there's no cross-rank communication/validations.
All of these two APIs stay private until it stablizes and proof of UX. The second one can only be called on `ShardedTensor` class directly, not included as a package API for now.
Test Plan:
test_init_from_local_shards_and_global_metadata
test_init_from_local_shards_and_global_metadata_invalid_shards
Reviewed By: dstaay-fb, pritamdamania87
Differential Revision: D32746882
fbshipit-source-id: bafd26ce16c02e2095907f9e59984a5d775c7df5
