HLSL: allow non-vec3 tessellation coordinate declarations

HLSL requires vec2 tessellation coordinate declarations in some cases
(e.g, isoline topology), where SPIR-V requires the TessCoord qualified
builtin to be a vec3 in all cases.  This alters the IO form of the
variable to be a vec3, which will be copied to the shader's declared
type if needed.  This is not a validation; the shader type must be correct.

hlsl/hlslParseHelper.h

@@ -250,7 +250,7 @@ protected:
     void addInterstageIoToLinkage();
     void addPatchConstantInvocation();
 
-    void fixBuiltInArrayType(TType&);
+    void fixBuiltInIoType(TType&);
 
     void flatten(const TSourceLoc& loc, const TVariable& variable);
     int flatten(const TSourceLoc& loc, const TVariable& variable, const TType&, TFlattenData&, TString name);