[clang] [HLSL] Implement SV_GroupID semantic (PR #115911)

[Damyan Pepper via cfe-commits]

https://github.com/damyanp commented:

This LGTM, but I think we should try and get reviews from @tex3d and @llvm-beanz before completing this PR.

https://github.com/llvm/llvm-project/pull/115911