swipeTracker: Calculate velocity using scroll history

swipeTracker: Calculate velocity using scroll history

In some cases we may get anevent with very low delta at the end of the
swipe. While we can't completely ignore them, we can smooth them using a
scroll history, similarly to what GTK kinetic scrolling does: keep track
of the last 150ms of events, and sum their deltas when calculating the
velocity.

The logic is based on what GTK does in GtkGestureSwipe and
GtkEventControllerScroll.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1647>