Add saving collection groups. Add open all and close all menu buttons for collections.

Source/Editor/CustomEditors/Elements/Container/GroupElement.cs

@@ -1,5 +1,7 @@
 // Copyright (c) 2012-2024 Wojciech Figat. All rights reserved.
 
+using System;
+using FlaxEditor.GUI.ContextMenu;
 using FlaxEngine;
 using FlaxEngine.GUI;
 
@@ -24,6 +26,11 @@ namespace FlaxEditor.CustomEditors.Elements
             EnableContainmentLines = true,
         };
 
+        /// <summary>
+        /// Event is fired if the group can setup a context menu and the context menu is being setup.
+        /// </summary>
+        public Action<ContextMenu, DropPanel> SetupContextMenu;
+
         /// <inheritdoc />
         public override ContainerControl ContainerControl => Panel;