QMenu should have a 'canceled' signal

QMenu is currently lacking a canceled (or rejected) signal that is emitted when the menu is closed but no action has been triggered. This happens when the user clicks outside the menu, for example.

In this case the aboutToHide signal is emitted, but that's not enough, since this signal is emitted also when the user triggers a menu action (so there is no easy way to distinguish the two scenarios: triggered vs canceled).