SwipeTracker connects to signals of the stage, but doesn't disconnect on
destroy, leaving them hanging and potentially running callbacks for
destroyed objects.
This is visible when removing a folder by dragging all icons out, and
running the swipe gestures, which will produce a bunch of warnings.
Explicitly destroy, remove, and disconnect the swipe tracker.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1518>
Add a unified swipe tracker supporting dragging, four-finger swipe on both
touchscreen and touchpad, and touchpad scrolling.
The shared logic is largely same as the one in WebKit and libhandy.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/826
