[clang] [llvm] [HLSL][DXIL] Implement `refract` intrinsic (PR #136026)

[Farzon Lotfi via cfe-commits]

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@@ -26,6 +26,12 @@ def SPIRVReflect : Builtin {
   let Prototype = "void(...)";
 }
 
+def SPIRVRefract : Builtin {
+  let Spellings = ["__builtin_spirv_refract"];
+  let Attributes = [NoThrow, Const];
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farzonl wrote:

You need to add `CustomTypeChecking`.
```suggestion
  let Attributes = [NoThrow, Const, CustomTypeChecking];
```

https://github.com/llvm/llvm-project/pull/136026