[clang] [HLSL] Implement TextureCube resource type (PR #218520)

[Helena Kotas via cfe-commits]

================
@@ -296,6 +296,32 @@ static BuiltinTypeDeclBuilder setupRWTextureType(CXXRecordDecl *Decl, Sema &S,
       .addStaticInitializationFunctions(false);
 }
 
+/// Set up TextureCube type: SRV cube texture. Locations are float3 direction
+/// vectors into the cube rather than texel coordinates, so cube textures have
+/// no Load, no operator[] and no mips member. Their sampling and gather
+/// methods also have no offset overloads.
+static BuiltinTypeDeclBuilder setupTextureCubeType(CXXRecordDecl *Decl,
+                                                   Sema &S) {
+  const ResourceDimension Dim = ResourceDimension::Cube;
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hekota wrote:

```suggestion
  constexpr ResourceDimension Dim = ResourceDimension::Cube;
```
This can be constexpr as well. I assume the IsArray variable will become a function arg in the next PR.

https://github.com/llvm/llvm-project/pull/218520