A TearoffMenuItem is a special MenuItem which is used to tear off and
reattach its menu.
When its menu is shown normally, the TearoffMenuItem is drawn as a
dotted line indicating that the menu can be torn off. Activating it causes
its menu to be torn off and displayed in its own window as a tearoff menu.
When its menu is shown as a tearoff menu, the TearoffMenuItem is drawn
as a dotted line which has a left pointing arrow graphic indicating that the
tearoff menu can be reattached. Activating it will erase the tearoff menu