libweston-desktop/xwayland: XWAYLAND surfaces are never 'added'

Add documentation (asserts) that show that windows of types XWAYLAND are
never registered with the shell.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>
1 file changed