Replace output screen size callback with transform helpers

Replace output screen size callback with transform helpers

Instead of automatically transforming absolute coordinates of touch and
pointer events to screen coordinates, the user now uses the corresponding
transform helper function. This means the coordinates returned by
libinput_event_pointer_get_absolute_x(),
libinput_event_pointer_get_absolute_y(), libinput_touch_get_x() and
libinput_touch_get_y() has changed from being in output screen coordinate
space to being in device specific coordinate space.

For example, where one before would call libinput_event_touch_get_x(event),
one now calls libinput_event_touch_get_x_transformed(event, output_width).

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>