[shard] Add deepcopy for ShardedTensor
This PR adding deep copy support a ShardedTensor. Sometimes user might want to deep copy a ShardedTensor param for comparision purpose.
Differential Revision: [D36084109](https://our.internmc.facebook.com/intern/diff/D36084109/)
**NOTE FOR REVIEWERS**: This PR has internal Facebook specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D36084109/)!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76758
Approved by: https://github.com/pritamdamania87, https://github.com/fduwjj
