Update PrefabStageUtility's new namespace

Author: keveleigh

Assets/MRTK/Core/Inspectors/Utilities/InspectorUIUtility.cs

@@ -650,7 +650,11 @@ static public bool DrawScriptableFoldout<T>(SerializedProperty scriptable, strin
                     else
                     {
                         bool isNestedInCurrentPrefab = false;
-                        var prefabStage = PrefabStageUtility.GetCurrentPrefabStage();
+#if UNITY_2021_2_OR_NEWER
+                        var prefabStage = UnityEditor.SceneManagement.PrefabStageUtility.GetCurrentPrefabStage();
+#else
+                        var prefabStage = UnityEditor.Experimental.SceneManagement.PrefabStageUtility.GetCurrentPrefabStage();
+#endif
                         if (prefabStage != null)
                         {
                             var instancePath = AssetDatabase.GetAssetPath(scriptable.objectReferenceValue);

Assets/MRTK/Core/Utilities/Scenes/EditorSceneUtils.cs

@@ -253,7 +253,11 @@ public static IEnumerable<GameObject> GetRootGameObjectsInLoadedScenes()
         /// </summary>
         public static bool IsEditingPrefab()
         {
+#if UNITY_2021_2_OR_NEWER
+            var prefabStage = UnityEditor.SceneManagement.PrefabStageUtility.GetCurrentPrefabStage();
+#else
             var prefabStage = UnityEditor.Experimental.SceneManagement.PrefabStageUtility.GetCurrentPrefabStage();
+#endif
             return prefabStage != null;
         }