At the moment, it's possible to activate a qtquick effect while another
qtquick effect is already active, we have code that prevents fullscreen
effects overriding each other, yet that still happens.

The reason for that behavior is that the gesture recognizer will mark
all gestures as started when user starts swiping on touchpad and cancel
gestures as more swiping occurs. This can mistrigger toggling logic in
the window view effect and the desktop grid effect, etc.

In order to make handling of gesture cancellation correct, we could
check whether user has swiped enough to deactivate window view, or
desktop grid. This change tries to implement exactly that.

As a side-effect, it also allows toggling the effect with the same
gesture. However, we should make cancellation gestures opposite of
activation gestures, i.e. if 4 swipe up gesture is used to activate an
effect, then 4 swipe down gesture should be used to deactivate the
effect.