Make XXXGUI class public

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Material/LayeredLit/LayeredLitUI.cs

 
 namespace UnityEditor.Experimental.Rendering.HDPipeline
 {
-    internal class LayeredLitGUI : LitGUI
+    public class LayeredLitGUI : LitGUI
     {
         public enum VertexColorMode
         {

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Material/Lit/LitUI.cs

 
 namespace UnityEditor.Experimental.Rendering.HDPipeline
 {
-    class LitGUI : BaseLitGUI
+    public class LitGUI : BaseLitGUI
     {
         protected static class Styles
         {