[llvm] Lower llvm.dx.rawBufferLoad to dxil ops (PR #116845)

[Zhengxing li via llvm-commits]

lizhengxing wrote:

> @lizhengxing - looks like there's some conflicts that need resolving before completing this. The description mentions it is a draft. Is this PR still something you want us to review and take in?

No, there's no review needed for this draft PR. I'll re-work the PR based on Justin's feedback.

https://github.com/llvm/llvm-project/pull/116845