Re-enabling a disabled Menu when using the system MenuBar on MacOS fails for the top level menuItems, that remain disabled, and only works as expected for submenus (and their possible menuItems), that are enabled.

See test attached. It can be reproduced with JavaFX 11.0.2, 17-ea+3 or head.

How to reproduce:

- Run the test
- Open the menu (all menus are enabled as expected)
- Click the button, a dialog will show. Open the menu (all menus are disabled as expected)
- Close the dialog. Open the menu ( "Sub-menu" and its item is enabled as expected but "Top Level Menu Item" is still disabled which is unexpected).
- Switch to other application and then switch back to the test. Open the menu (all menu items are enabled again, as expected).