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

[Deric C. via cfe-commits]

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Icohedron wrote:

If you add a test here that uses `half`
```c++
half4 test_lit_half(half NDotL, half NDotH, half M) { return lit(NDotL, NDotH, M); }
```
Will it convert the `half` types to float?

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