Refactor API validation code to actually check that each define is

indeed define, this prevents platforms from going out of sync.

Assets/ScriptableRenderLoop/ShaderLibrary/API/D3D11.hlsl

-#ifndef UNITY_D3D11_INCLUDED
-#define UNITY_D3D11_INCLUDED
-
-#define UNITY_UV_STARTS_AT_TOP 1
-
-#endif // UNITY_D3D11_INCLUDED
+#define UNITY_UV_STARTS_AT_TOP 1

Assets/ScriptableRenderLoop/ShaderLibrary/API/D3D11_1.hlsl

-#ifndef UNITY_D3D11_INCLUDED
-#define UNITY_D3D11_INCLUDED
-
-#define UNITY_UV_STARTS_AT_TOP 1
-
-#endif // UNITY_D3D11_INCLUDED
+#define UNITY_UV_STARTS_AT_TOP 1

Assets/ScriptableRenderLoop/ShaderLibrary/Common.hlsl

 #include "API/D3D11.hlsl"
 #elif defined(SHADER_API_XBOXONE)
 #include "API/D3D11_1.hlsl"
+#else
+unsupported shader api
 #endif
 
 // ----------------------------------------------------------------------------

Assets/ScriptableRenderLoop/ShaderLibrary/API/Validate.hlsl

+// Upgrade NOTE: replaced 'defined in' with 'defined (in)'
+
+#define REQUIRE_DEFINED(X_) \
+	#ifndef X_  \
+		#error X_ must be defined (in) the platform include \
+	#endif X_  \
+
+REQUIRE_DEFINED(UNITY_UV_STARTS_AT_TOP)