Override DockWidget::setParentView() instead of relying on QEvent

So it works with non-Qt frontends too.

src/controllers/DockWidget.cpp

@@ -71,7 +71,6 @@ void DockWidget::init()
 {
     d->init();
     view()->setAttribute(Qt::WA_PendingMoveEvent, false);
-    view()->d->parentChanged.connect(&Private::onParentChanged, d);
 }
 
 void DockWidget::addDockWidgetAsTab(DockWidget *other, InitialOption option)
@@ -513,6 +512,12 @@ Controllers::DockWidget *DockWidget::byName(const QString &uniqueName)
     return DockRegistry::self()->dockByName(uniqueName);
 }
 
+void DockWidget::setParentView(View *parent)
+{
+    Controller::setParentView(parent);
+    d->onParentChanged();
+}
+
 bool DockWidget::skipsRestore() const
 {
     return d->layoutSaverOptions & LayoutSaverOption::Skip;