scrolledwindow: Cancel overshoot on dimension changes

scrolledwindow: Cancel overshoot on dimension changes

If we scroll down in a list that's still being filled, we hit the edge and
initiate overshoot, and then the adjustment's upper value increases. This
leads to an unwanted bounce back.

Additionally, if in a similar situation the upper value decreases, the
overscroll glow gets stuck.

Update kinetic scrolling upper and lower value on changes, and immediately
cancel it if dimensions on that side change.

Fixes https://gitlab.gnome.org/GNOME/gtk/-/issues/3752