[clang] [HLSL] Add matrix support to atan2 (PR #194984)

[Farzon Lotfi via cfe-commits]

farzonl wrote:

hmm I was expecting to see a change in `clang/include/clang/Basic/HLSLIntrinsics.td`? I'm guessing we were implicilty generating matrix signatures just not testing it?

 cc: @Icohedron

https://github.com/llvm/llvm-project/pull/194984