create type hint stub files for module torch (#12500)

Summary:
We have:

- This is an initial stab at creating a type stub `torch/__init__.pyi` .
- This is only tested on Python 3, since that's the only Python version mypy
  works on.
- So far, we only aim at doing this for torch functions and torch.Tensor.
- Quite a few methods and functions have to be typed manually. These are
  done in `torch/__init__.pyi.in`

For me, PyCharm (the non-paid one) didn't seem to indicate errors in the .pyi when opening and seemed to be able to get the type hint for the few functions I tried, but I don't use PyCharm for my usual PyTorch activities, so I didn't extensively try this out.

An example of a generated PYI is at [this gist](https://gist.github.com/ezyang/bf9b6a5fa8827c52152858169bcb61b1).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/12500

Differential Revision: D13695553

Pulled By: ezyang

fbshipit-source-id: 4566c71913ede4e4c23ebc4a72c17151f94e8e21

1 files changed, 1 insertions, 0 deletions

diff --git a/setup.py b/setup.py
index 465ed78a39..9b79d79801 100644
--- a/setup.py
+++ b/setup.py
@@ -731,6 +731,7 @@ if __name__ == '__main__':
         entry_points=entry_points,
         package_data={
             'torch': [
+                '__init__.pyi',
                 'lib/*.so*',
                 'lib/*.dylib*',
                 'lib/*.dll',