[clang] [HLSL] Implement the HLSL distance intrinsic (PR #122357)

[Farzon Lotfi via cfe-commits]

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@@ -871,6 +871,34 @@ float3 degrees(float3);
 _HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_degrees)
 float4 degrees(float4);
 
+//===----------------------------------------------------------------------===//
+// distance builtins
+//===----------------------------------------------------------------------===//
+
+/// \fn K distance(T X, T Y)
+/// \brief Returns a distance scalar between two vectors of \a X and \a Y.
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farzonl wrote:

This comment is for the whole set of  distance overloads. We have never commented per function to this point. 

https://github.com/llvm/llvm-project/pull/122357