core-view: Fix pointer input on touch
The combination of GtkGestureClick+GtkEventControllerMotion was a naive direct port from GTK3's event signals. However, it can't really work on touchscreen: motion events never happen.
Instead, use a GtkGestureDrag to track the whole press-drag-release sequence at once, and only use GtkEventControllerMotion when not dragging.
Edited by Alice Mikhaylenko