[FSDP][optim_state_dict] Consolidate rank0_only load logic (#99647)
Follow up https://github.com/pytorch/pytorch/pull/99624, this PR consolidate the logic of `use_orig_params=False` with `use_orig_params=True` to use the same logic to load optimizer checkpoint when rank0_only is True.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99647
Approved by: https://github.com/wz337
