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>
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