Fix clazy warnings in QPointingDevice::grabChanged signal

- a signal does not need to be marked const; but fixing it would be BIC,
  so has to wait until Qt 7
- QPointingDevice::GrabTransition should be fully qualified
- wrap the long line while we're at it

Amends 2692237bb1

Change-Id: I5d518bbbcb62d336bae0d59647b16018d83b9479
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/gui/kernel/qpointingdevice.h

@@ -107,7 +107,12 @@ public:
     bool operator==(const QPointingDevice &other) const;
 
 Q_SIGNALS:
-    void grabChanged(QObject *grabber, GrabTransition transition, const QPointerEvent *event, const QEventPoint &point) const;
+    void grabChanged(QObject *grabber, QPointingDevice::GrabTransition transition,
+                     const QPointerEvent *event, const QEventPoint &point)
+#if QT_VERSION < QT_VERSION_CHECK(7, 0, 0)
+    const
+#endif
+    ;
 
 protected:
     QPointingDevice(QPointingDevicePrivate &d, QObject *parent);