qtquick: DockWidget now receives QQmlEngine as param

If nullptr then the usual Config::qmlEngine() will be used.

src/DockWidgetQuick.cpp

@@ -48,9 +48,10 @@ public:
     QQmlEngine *const m_qmlEngine;
 };
 
-DockWidgetQuick::DockWidgetQuick(const QString &name, Options options, LayoutSaverOptions layoutSaverOptions)
+DockWidgetQuick::DockWidgetQuick(const QString &name, Options options,
+                                 LayoutSaverOptions layoutSaverOptions, QQmlEngine *engine)
     : DockWidgetBase(name, options, layoutSaverOptions)
-    , d(new Private(this, Config::self().qmlEngine()))
+    , d(new Private(this, engine ? engine : Config::self().qmlEngine()))
 {
     // To mimic what QtWidgets does when creating a new QWidget.
     setVisible(false);

src/DockWidgetQuick.h

@@ -23,6 +23,7 @@
 
 QT_BEGIN_NAMESPACE
 class QCloseEvent;
+class QQmlEngine;
 QT_END_NAMESPACE
 
 namespace KDDockWidgets {
@@ -44,12 +45,16 @@ public:
      * @brief constructs a new DockWidget
      * @param uniqueName the name of the dockwidget, should be unique. Use title for user visible text.
      * @param options optional options controlling behaviour
+     * @param layoutSaverOptions options regarding LayoutSaver behaviour
+     * @param engine the QML engine this dock widget will be created on. If not specified then
+     * Config::self().qmlEngine() will be used
      *
      * There's no parent argument. The DockWidget is either parented to FloatingWindow or MainWindow
      * when visible, or stays without a parent when hidden.
      */
     explicit DockWidgetQuick(const QString &uniqueName, Options options = {},
-                             LayoutSaverOptions layoutSaverOptions = LayoutSaverOptions());
+                             LayoutSaverOptions layoutSaverOptions = LayoutSaverOptions(),
+                             QQmlEngine *engine = nullptr);
 
     ///@brief destructor
     ~DockWidgetQuick() override;

src/private/quick/DockWidgetInstantiator.cpp

@@ -179,7 +179,7 @@ void DockWidgetInstantiator::componentComplete()
         return;
     }
 
-    m_dockWidget = new DockWidgetQuick(m_uniqueName);
+    m_dockWidget = new DockWidgetQuick(m_uniqueName, {}, {}, qmlEngine(this));
 
     connect(m_dockWidget, &DockWidgetQuick::titleChanged, this,
             &DockWidgetInstantiator::titleChanged);