Cocoa Menu: Set keyboard modifiers when item is activated

Seems to be a regression from 4.8, which is not surprising
since everything was rewritten for QPA.

Task-number: QTBUG-36851
Change-Id: If89f8c9e6897fd1e02800f49e51baeb1ea181238
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>
Reviewed-by: James Turner <james.turner@kdab.com>

src/plugins/platforms/cocoa/qcocoamenu.mm

@@ -127,6 +127,7 @@ QT_NAMESPACE_ALIAS_OBJC_CLASS(QCocoaMenuDelegate);
 {
     QCocoaMenuItem *cocoaItem = reinterpret_cast<QCocoaMenuItem *>([item tag]);
     QScopedLoopLevelCounter loopLevelCounter(QGuiApplicationPrivate::instance()->threadData);
+    QGuiApplicationPrivate::modifier_buttons = [QNSView convertKeyModifiers:[NSEvent modifierFlags]];
     cocoaItem->activated();
 }