Propagate the event acceptance correctly with context menu on RMB

The context menu event created in QWidgetWindow::handleMouseEvent
does not forward its acceptance flag on which a client may rely.

Task-number: QTBUG-106389
Backport-to: 6.4 6.4.0
Change-Id: I17a53ebd23b4ae0a2721c629f3ecc7aeec56233d
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/widgets/kernel/qwidgetwindow.cpp

@@ -629,6 +629,8 @@ void QWidgetWindow::handleMouseEvent(QMouseEvent *event)
         && m_widget->rect().contains(event->position().toPoint())) {
         QContextMenuEvent e(QContextMenuEvent::Mouse, mapped, event->globalPosition().toPoint(), event->modifiers());
         QGuiApplication::forwardEvent(receiver, &e, event);
+        if (e.isAccepted())
+            event->accept();
     }
 #endif
 }