Add typing for torch.return_type
Currently, `NamedTuple` return types are created in `torch/_VF.pyi` instead of
typing being added for the symbols in in `torch/return_types.py`. This also
fixes the type names to match the actual names in the python code.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74199
Approved by: https://github.com/ezyang
