Show warning when VisualElement material is not compatible.

Author: ncerone-unity

Packages/com.unity.shadergraph/Editor/Generation/Targets/UITK/UISubTarget.cs

@@ -110,6 +110,7 @@ public virtual SubShaderDescriptor GenerateDefaultSubshader(bool isSRP = true )
                     shaderFallback = "",
                     CanUseSpriteAtlas = "True",
                     generatesPreview = true,
+                    customTags = "\"isCustomUITKShader\"=\"true\"",
                     passes = new PassCollection(),
 
                 };