[clang] [HLSL] Implement the `lit` intrinsic (PR #134171)

[Kaitlin Peng via cfe-commits]

================

----------------
kmpeng wrote:

I currently don't have `-fnative-half-type` enabled in that file, so yes this test case ends up having `float` input/return types (though it's not necessarily being converted in the function, if that's what you're asking). With `-fnative-half-type` enabled it doesn't convert to `float`

https://github.com/llvm/llvm-project/pull/134171