restore old documentation references (#39086)
Summary:
Fixes gh-39007
We replaced actual content with links to generated content in many places to break the documentation into manageable chunks. This caused references like
```
https://pytorch.org/docs/stable/torch.html#torch.flip
```
to become
```
https://pytorch.org/docs/master/generated/torch.flip.html#torch.flip
```
The textual content that was located at the old reference was replaced with a link to the new reference. This PR adds a `<p id="xxx"/p>` reference next to the link, so that the older references from outside tutorials and forums still work: they will bring the user to the link that they can then follow through to see the actual content.
The way this is done is to monkeypatch the sphinx writer method that produces the link. It is ugly but practical, and in my mind not worse than adding javascript to do the same thing.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39086
Differential Revision: D22462421
Pulled By: jlin27
fbshipit-source-id: b8f913b38c56ebb857c5a07bded6509890900647
