[clang] [llvm] [HLSL] Add initial support for output semantics (PR #168095)

[Steven Perron via llvm-commits]

https://github.com/s-perron approved this pull request.

LGTM. Minor issues. The main one is the codegen test could check that the metadata declaring the location decoration is correct.

https://github.com/llvm/llvm-project/pull/168095