Partially revert "Move notification of layout change up from QApplication to QGuiApplication."

We can't rely on QGuiApplication::topLevelWindows containing top level QWidgets,
because they only exist as actual windows once QWidgetPrivate::create_sys is
called. Thus, make sure to send notifications to all top level widgets, if a
QApplication is being used.

This reverts commit f82ed5b3e30282bb8dc1da321a0d04ad4d463e59.

Task-number: QTBUG-35589
Change-Id: Iac517089af1c22f20094ba6e185d5ed44ebe3d6f
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/widgets/kernel/qapplication.cpp

@@ -1888,6 +1888,31 @@ bool QApplication::event(QEvent *e)
     \obsolete
 */
 
+// ### FIXME: topLevelWindows does not contain QWidgets without a parent
+// until create_sys is called. So we have to override the
+// QGuiApplication::notifyLayoutDirectionChange
+// to do the right thing.
+void QApplicationPrivate::notifyLayoutDirectionChange()
+{
+    const QWidgetList list = QApplication::topLevelWidgets();
+    QWindowList windowList = QGuiApplication::topLevelWindows();
+
+    // send to all top-level QWidgets
+    for (int i = 0; i < list.size(); ++i) {
+        QWidget *w = list.at(i);
+        windowList.removeAll(w->windowHandle());
+        QEvent ev(QEvent::ApplicationLayoutDirectionChange);
+        QCoreApplication::sendEvent(w, &ev);
+    }
+
+    // in case there are any plain QWindows in this QApplication-using
+    // application, also send the notification to them
+    for (int i = 0; i < windowList.size(); ++i) {
+        QEvent ev(QEvent::ApplicationLayoutDirectionChange);
+        QCoreApplication::sendEvent(windowList.at(i), &ev);
+    }
+}
+
 /*!
     \fn void QApplication::setActiveWindow(QWidget* active)
 

src/widgets/kernel/qapplication_p.h

@@ -116,6 +116,7 @@ public:
     QApplicationPrivate(int &argc, char **argv, int flags);
     ~QApplicationPrivate();
 
+    virtual void notifyLayoutDirectionChange();
     virtual void notifyActiveWindowChange(QWindow *);
 
     virtual bool shouldQuit();