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This is replaced by GtkGestureLongPress, and all its callers have
been updated to use the replacement.

This is somewhat analogous to scroll events on pointer devices, the
greater the velocity, the faster the spinbutton spins.

This gesture reports events on horizontal/vertical panning gestures.

This can be used to fetch the current velocity on update(), as opposed
to swipe() which happens after the sequence is finished.

GtkGestureLongPress and GtkGestureMultiPress are both used
to replace it.

Instead do so on button release, or after text selection dragging
starts.

And delegate on GtkGesture::check(), it does deal better with
extra fleeting touches.