Remove RES and REF typedefs in favor of spelled out Ref<>

These typedefs don't save much typing compared to the full `Ref<Resource>`
and `Ref<RefCounted>`, yet they sometimes introduce confusion among
new contributors.

editor/editor_data.h

@@ -46,7 +46,7 @@ class EditorPlugin;
 class EditorSelectionHistory {
 	// Stores the object & property (if relevant).
 	struct _Object {
-		REF ref;
+		Ref<RefCounted> ref;
 		ObjectID object;
 		String property;
 		bool inspector_only = false;