Signals: Fix some regressions from #36426

- Fix `callable_mp` bindings to methods which used to have default
  arguments passed to `bind_method`. We now have to re-specify them
  manually when connecting.
- Re-add `GroupsEditor::update_tree` binding.
- Misc code quality changes along the way.

editor/filesystem_dock.h

@@ -222,7 +222,7 @@ private:
 	void _duplicate_operation_confirm();
 	void _move_with_overwrite();
 	bool _check_existing();
-	void _move_operation_confirm(const String &p_to_path, bool overwrite = false);
+	void _move_operation_confirm(const String &p_to_path, bool p_overwrite = false);
 
 	void _tree_rmb_option(int p_option);
 	void _file_list_rmb_option(int p_option);