protocol: add weston_touch_calibration

This is a Wayland protocol extension to allow the calibration of
touchscreens in Weston.

See: https://phabricator.freedesktop.org/T7868



v2:
- replace "server" with "compositor"
- rephrase error conditions to be simpler
- reword the matrix description in 'save' request
- rephrase when touch_device events are sent
- change device id to DEVPATH with "/sys" prefix
- qualify calibration units better
- replace wrong_touch event with a more generic invalid_touch
- fix error enum and add bad_coordinates
- convert while cancelled will not raise any errors

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>