Signals: Port more uses of connect_compat

Those were problematic as they call a method of their parent class,
but callable_mp does not allow that unless it's public.

To solve it, we declare a local class that calls the parent class'
method, which now needs to be protected to be accessible in the
derived class.

editor/create_dialog.h

@@ -60,6 +60,7 @@ class CreateDialog : public ConfirmationDialog {
 	Set<StringName> type_blacklist;
 
 	void _item_selected();
+	void _hide_requested();
 
 	void _update_search();
 	void _update_favorite_list();