TabBar controller now stores the current dock widget

It's no longer stored in the view.
This makes it easier for new frontends.

src/qtquick/views/TabBar_qtquick.h

@@ -56,8 +56,6 @@ public:
     QRect rectForTab(int index) const override;
 
     void moveTabTo(int from, int to) override;
-    Controllers::DockWidget *currentDockWidget() const override;
-    int currentIndex() const override;
     Q_INVOKABLE void setCurrentIndex(int index) override;
     bool tabsAreMovable() const override;
     Stack_qtquick *stackView() const;