Fix ignoring closeEvents on OSX for QtQuick.

The QCloseEvent's accepted state should not be inverted for the QWindowSystemInterfacePrivate::CloseEvent. To make Widgets work with this change, pass whether the close was accepted from close_helper to the QCloseEvent generated by QGuiApplication.
Task-number: QTBUG-28965

Change-Id: If384b0355776b93df02dff2ab78b5647903200e7
Merge commit '441f839' into st (amended commit message)