Port layoutInvalidated signal to KDBindings

This removes triplication between qtquick, qtwidgets and tests.
It also allows us to remove the usage of old-style Qt connect.

src/qtquick/views/Frame_qtquick.h

@@ -70,9 +70,6 @@ protected:
 Q_SIGNALS:
     void tabTitlesChanged();
 
-    // TODOv2: It's duplicated with Frame_qtwidgets, port to views/Frame.h as KDSignal
-    void layoutInvalidated();
-
 public Q_SLOTS:
     void updateConstriants();