Make Module::register_module / register_parameter / register_buffer public (#23196)
Summary:
In Python, `register_module` / `register_parameter` / `register_buffer` method in `nn.Module` is public. This PR makes those APIs public for C++ `nn::Module` as well. Closes https://github.com/pytorch/pytorch/issues/23140.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23196
Differential Revision: D16440239
Pulled By: yf225
fbshipit-source-id: e0eff6e1db592961fba891ec417dc74fa765e968
