[FSDP] Make set_state_type to SHARDED_STATE_DICT compatible with NO_SHARD sharding_strategy (#100208)
Currently, if we use NO_SHARD strategy for fully_shard and set state_dict_type to be SHARDED_STATE_DICT, a runtime error would be raised ("``sharded_state_dict`` can only be used when parameters are flatten and sharded.").
This PR updates pre_state_dict_hook, post_state_dict_hook, pre_load_state_dict_hook, and post_load_state_dict_hook to set state_dict_type and state_dict_config to full state when using NO_SHARD, even if the state_dict_type and state_dict_config of the root module is set to sharded state.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100208
Approved by: https://github.com/rohan-varma
