Forward rejected key events to the next responder by checking the return value from QWindowSystemInterface and calling the superclass event handler. This is useful when Qt is running as a plugin in a host application; the host can now react to key events even if Qt has focus. Qt will often not accept keyUp events, even if the corresponding keyDown was accepted, for example in the case of text controls. We don't want to forward 'bare' keyUps, so keep track of which keyDowns have been seen. Change-Id: I976448a5d305a657a0e91aeb271b158f8b598286 Task-number: QTBUG-45768 Reviewed-by: Timur Pocheptsov <timur.pocheptsov@theqtcompany.com>