HDRenderPipeline: Fix upgrader class access

ScriptableRenderPipeline/HDRenderPipeline/Editor/Material/Lit/StandardSpecularToHDLitMaterialUpgrader.cs

 
 namespace UnityEditor.Experimental.Rendering.HDPipeline
 {
-    class StandardSpecularToHDLitMaterialUpgrader : MaterialUpgrader
+    public class StandardSpecularToHDLitMaterialUpgrader : MaterialUpgrader
     {
         public StandardSpecularToHDLitMaterialUpgrader() : this("Standard (Specular setup)", "HDRenderPipeline/Lit", LitGUI.SetupMaterialKeywordsAndPass) {}
 

ScriptableRenderPipeline/HDRenderPipeline/Editor/Material/Lit/StandardToHDLitMaterialUpgrader.cs

 
 namespace UnityEditor.Experimental.Rendering.HDPipeline
 {
-    class StandardToHDLitMaterialUpgrader : MaterialUpgrader
+    public class StandardToHDLitMaterialUpgrader : MaterialUpgrader
     {
         public StandardToHDLitMaterialUpgrader() : this("Standard", "HDRenderPipeline/Lit", LitGUI.SetupMaterialKeywordsAndPass) {}