Louis-Francis Ratté-Boulianne authored Nov 28, 2017 and Pekka Paalanen committed May 30, 2018

Introduce weston_touch_device for libweston core to track individual
touchscreen input devices. A weston_seat/weston_touch may be an
aggregation of several physical touchscreen input devices. Separating
the physical devices will be required for implementing touchscreen
calibration. One can only calibrate one device at a time, and we want to
make sure to handle the right one.

Both backends that support touch devices are updated to create
weston_touch_devices. Wayland-backend provides touch devices that cannot
be calibrated, because we have no access to raw touch coordinates from
the device - calibration is the responsibility of the parent display
server. Libinput backend provides touch devices that can be calibrated,
hence implementing the set and get calibration hooks.

Backends need to maintain an output pointer in any case, so we have a
get_output() hook instead of having to maintain an identical field in
weston_touch_device. The same justification applies to
get_calibration_head_name.

Also update the test plugin to manage weston_touch_device objects.

Co-developed by Louis-Francis and Pekka.

v2:
- Consistently use 'cal' instead of 'calb' or 'matrix'.
- change devpath into syspath
- update copyrights

Signed-off-by: Louis-Francis Ratté-Boulianne <lfrb@collabora.com>
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
v1 Tested-by: Matt Hoosier <matt.hoosier@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>