indicators: Depend less on FloatingWindow

Deal in terms of WindowBeingDragged instead, as wayland won't have
a floating window being dragged

src/private/DragController.cpp

@@ -389,7 +389,7 @@ void DragController::releaseMouse(QWidgetOrQuick *target)
     }
 }
 
-FloatingWindow *DragController::windowBeingDragged() const
+FloatingWindow *DragController::floatingWindowBeingDragged() const
 {
     return m_windowBeingDragged ? m_windowBeingDragged->floatingWindow()
                                 : nullptr;
@@ -401,6 +401,11 @@ void DragController::enableFallbackMouseGrabber()
         m_fallbackMouseGrabber = new FallbackMouseGrabber(this);
 }
 
+WindowBeingDragged *DragController::windowBeingDragged() const
+{
+    return m_windowBeingDragged.get();
+}
+
 static QMouseEvent *mouseEvent(QEvent *e)
 {
     switch (e->type()) {