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

[Deric Cheung via llvm-commits]

Icohedron wrote:

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

I just created issue #123831 for this.

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