[clang] [HLSL] Fix resource wrapper declaration (PR #125718)

[Chris B via cfe-commits]

https://github.com/llvm-beanz commented:

I have a couple concerns about this approach. I'm curious for @bogner's thoughts since he has approved the PR.

1) If/when we support separate compilation, the user-facing exported "resource" object will be the resource wrapper, not the handle, so that indicates to me we should probably have the wrappers being public.
2) It feels wrong to do this in CodeGen. It seems like we should be identifying an appropriate storage class in Sema such that we assign the correct linkage automatically.

@hekota might also have some good insights here because she is dealing with some of HLSL's implicit storage class/address space nonsense in her work with cbuffers.

https://github.com/llvm/llvm-project/pull/125718