Draft: Use drag-surface

Hacked that up during Debcamp and completely forgot:

This

• moves the animation to the compositor side
• allows to swipe away the keyboard

Marking as draft as I need to fix a couple of things (which I think need some fixes on the phoc side):

• fix the exclusive zone as otherwise the OSK isn't rendered at the bottom of the screen in the overview
• fix rendering on the lock screen
• maybe: allow to fine tune the drag threshold (when we start to recognize a drag)
• disable drag with pipe based completer as it would break swipe input