[clang] [llvm] [HLSL] Implement the `degrees` intrinsic (PR #111209)

[Finn Plummer via cfe-commits]

inbelic wrote:

Rebasing onto commit that allows the use of `selectExtInst` with both `CL::degrees` and `GL::Degrees`. Adding additional testcase for this as well.

https://github.com/llvm/llvm-project/pull/111209