Add CustomUpscale postFx to replace upscaler with a custom script

Source/Engine/Graphics/Enums.h

@@ -609,6 +609,9 @@ API_ENUM() enum class MaterialPostFxLocation : byte
     /// The 'after' AA filter pass. Rendering is done to the output backbuffer.
     /// </summary>
     AfterAntiAliasingPass = 5,
+
+    API_ENUM(Attributes="HideInEditor")
+    MAX,
 };
 
 /// <summary>
@@ -637,9 +640,17 @@ API_ENUM() enum class PostProcessEffectLocation
     BeforeReflectionsPass = 3,
 
     /// <summary>
-    /// The 'after' AA filter pass. Rendering is done to the output backbuffer.
+    /// The 'after' AA filter pass.
     /// </summary>
     AfterAntiAliasingPass = 4,
+
+    /// <summary>
+    /// The custom frame up-scaling that replaces default implementation. Rendering is done to the output backbuffer (use OutputView and OutputViewport as render destination).
+    /// </summary>
+    CustomUpscale = 5,
+
+    API_ENUM(Attributes="HideInEditor")
+    MAX,
 };
 
 /// <summary>