[clang] [llvm] [HLSL] Implement the `reflect` HLSL function (PR #122992)

[Farzon Lotfi via llvm-commits]

farzonl wrote:

> Will a follow-up issue be created to move the useful `Sema` helpers into a common file?

I'm fine if you want to do this as a follow up.


https://github.com/llvm/llvm-project/pull/122992