Added Config::Flag_KeepAboveIfNotUtilityWindow

Which sets Qt::WindowStaysOnTopHint for floating windows.
Usually unneeded, as floating windows are Qt::Tool with a transient
parent, but in case you're using Flag_DontUseUtilityFloatingWindows
then you might want (or not) to keep them above.

src/private/quick/QWidgetAdapter_quick.cpp

@@ -397,6 +397,12 @@ QSize QWidgetAdapter::sizeHint() const
     return m_sizeHint;
 }
 
+void QWidgetAdapter::setWindowFlag(int flag, bool enable)
+{
+    Q_UNUSED(flag);
+    Q_UNUSED(enable);
+}
+
 Qt::WindowFlags QWidgetAdapter::windowFlags() const
 {
     return m_windowFlags;