libweston-desktop: Implement xdg_shell_v6

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
Reviewed-by: Jonas Ådahl <jadahl@gmail.com>
Acked-by: Giulio Camuffo <giulio.camuffo@kdab.com>

Differential Revision: https://phabricator.freedesktop.org/D1210
6 files changed