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

[Justin Bogner via cfe-commits]

bogner wrote:

@AaronBallman Do you think we should break out a new documentation category for either the resource attributes in particular or the HLSL attributes generally? I think these may feel kind of odd interspersed with the other docs for attributes on variables.

Also, is there a way to link into the attr docs? It might be nice to cross reference these from https://clang.llvm.org/docs/HLSL/ResourceTypes.html

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