Input refactors Pt.1
Some excision from wip/carlosg/input-thread. In this MR:
- Management of touch events (CANCEL specifically) are made simpler
- Which also allows the libinput event filter to go away.
- The management of relative motion filters, pointer constraints and barriers is centralized in the backend, without the need of external hook functions.
- ClutterInputDevice API gets sanitized, and drops its stage/time concepts, all towards making the object essentially const/readonly from public API.