[macos] Aqua LAF does not fire an action event if combo box menu is displayed

When the user types Enter in an editable combo box, Aqua LAF fails to fire an action event if the menu is displayed. Other LAFs that I have tested do fire an action event, as do native NSComboBox instances. (Actually, they fire two action events, but that is a separate issue.) That means the user must type Enter twice to get the desired effect of a single Enter when using the Aqua LAF. The first Enter dismisses the menu. The second Enter fires the event(s). See attached test program.