Verify that stdlib-reference docs can be used with readthedocs.io

[aidanfnv]

In order to move all of the Slang docs to readthedocs.io, we need to verify that the cross links and table contents work, and that there is a path forward for updating the bot to link this repo, the slang repo, and the readthedocs site together correctly.

[jkwak-work]

This issue is "In Review" state but I don't see a PR to review.
Is it this?

• Set up readthedocs in shader-slang.github.io shader-slang.github.io#71

[aidanfnv]

This is the PR for this issue: shader-slang/slang#6904

[aidanfnv]

Verified that these docs can be used, with some changed that were merged in shader-slang/slang#6904 and #4