qtquick: Implement DefaultWidgetFactory_qtquick

Requires implementing some pure-virtuals in the views too

src/qtquick/views/TabBar_qtquick.h

@@ -52,6 +52,8 @@ public:
     QRect rectForTab(int index) const override;
 
     void moveTabTo(int from, int to) override;
+    Controllers::DockWidget *currentDockWidget() const override;
+    bool tabsAreMovable() const override;
 
 Q_SIGNALS:
     void tabBarQmlItemChanged();