[clang] [llvm] [HLSL] Implement ddx/ddy_fine intrinsics (PR #168874)

[Sarah Spall via llvm-commits]

spall wrote:

> If all is good with this can you merge please? I don't have the permissions @spall Thanks!

I think we need another review; let me ping my team

https://github.com/llvm/llvm-project/pull/168874