[clang] [HLSL] Document all spellable attributes (PR #213346)

[Justin Bogner via cfe-commits]

bogner wrote:

> I have reservations about the newly added file and function, but I think the other files are fine.

What do you mean here? There is no newly added file or function. What reservations do you have? I don't understand what you're trying to say.

https://github.com/llvm/llvm-project/pull/213346