[clang] [llvm] [HLSL] Add semantic signature packing flags and invoke packing (PR #226554)

[via cfe-commits]

https://github.com/joaosaffran approved this pull request.

Approving the clang argument addition part. Deferring to others to approve the correctness of semantics packing logic, since I am not familiar with those.

https://github.com/llvm/llvm-project/pull/226554