[clang] [HLSL] Implement D3DCOLORtoUBYTE4 intrinsic (PR #122202)

[Finn Plummer via cfe-commits]

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@@ -33,6 +33,14 @@ constexpr enable_if_t<sizeof(U) == sizeof(T), U> bit_cast(T F) {
   return __builtin_bit_cast(U, F);
 }
 
+constexpr vector<uint, 4> d3d_color_to_ubyte4(vector<float, 4> V) {
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inbelic wrote:

```suggestion
constexpr vector<uint, 4> D3DColorToUByte4Impl(vector<float, 4> V) {
```
I think this follows more to how the length builtin was defined

https://github.com/llvm/llvm-project/pull/122202