Stubs for torch.nn (#19089)
Summary:
Closes https://github.com/pytorch/pytorch/issues/18724
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19089
Differential Revision: D16073654
Pulled By: ezyang
fbshipit-source-id: 5642179651ce45ab7c5a46cc1fcc4fd6b37fa71c
