[clang] [HLSL] Implement the dst HLSL Function (PR #133828)

[Ashley Coleman via cfe-commits]

================
@@ -174,6 +174,31 @@ const inline float distance(__detail::HLSL_FIXED_VECTOR<float, N> X,
                             __detail::HLSL_FIXED_VECTOR<float, N> Y) {
   return __detail::distance_vec_impl(X, Y);
 }
+//===----------------------------------------------------------------------===//
+// dst builtins
+//===----------------------------------------------------------------------===//
+
+/// \fn fvector dst( fvector, fvector)
----------------
V-FEXrt wrote:

```suggestion
/// \fn fvector dst(fvector, fvector)
```

https://github.com/llvm/llvm-project/pull/133828