Move nn.Module.load_state_dict tests from test_nn.py to separate file (#118028)
Move these tests out so in https://github.com/pytorch/pytorch/pull/117913 where we can to run these tests with both `torch.nn.utils.set_swap_module_params_on_conversion({True/False})`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/118028
Approved by: https://github.com/albanD
