Using env variable : OZONE_WAYLAND_USE_XDG_SHELL
Using env variable : OZONE_WAYLAND_USE_XDG_SHELL

(name is inspired from Qt and EFL implementations of xdg-shell)

So far xdg-shell is an extension to weston,
let's make it available at runtime
but make sure to have xdg-shell enabled also at buildtime.

Without this env variable defined (ie: in /etc/profile),
if no other alt shell is selected
then wl-shell will be used as (mandatory) fallback.

Signed-off-by: Philippe Coval <ff46fec9739d31cce915aabcc3a7a2c00eee4d6c@open.eurogiciel.org>

Tarnyko/ozone-wayland,clopez/ozone-wayland,mrunalk/ozone-wayland,AndriyP/ozone-wayland,kuscsik/ozone-wayland,AndriyP/ozone-wayland,sjnewbury/ozone-wayland,nagineni/ozone-wayland,Tarnyko/ozone-wayland,nagineni/ozone-wayland,01org/ozone-wayland,mrunalk/ozone-wayland,joone/ozone-wayland,kishansheshagiri/ozone-wayland,joone/ozone-wayland,sjnewbury/ozone-wayland,nagineni/ozone-wayland,01org/ozone-wayland,AndriyP/ozone-wayland,kishansheshagiri/ozone-wayland,baillaw/ozone-wayland,joone/ozone-wayland,baillaw/ozone-wayland,baillaw/ozone-wayland,baillaw/ozone-wayland,nicoguyo/ozone-wayland,01org/ozone-wayland,mrunalk/ozone-wayland,sjnewbury/ozone-wayland,siteshwar/ozone-wayland,clopez/ozone-wayland,siteshwar/ozone-wayland,sjnewbury/ozone-wayland,kuscsik/ozone-wayland,likewise/ozone-wayland,nicoguyo/ozone-wayland,shaochangbin/ozone-wayland,Tarnyko/ozone-wayland,kuscsik/ozone-wayland,nicoguyo/ozone-wayland,shaochangbin/ozone-wayland,AndriyP/ozone-wayland,kuscsik/ozone-wayland,shaochangbin/ozone-wayland,clopez/ozone-wayland,nicoguyo/ozone-wayland,likewise/ozone-wayland,kishansheshagiri/ozone-wayland,nagineni/ozone-wayland,likewise/ozone-wayland,siteshwar/ozone-wayland,likewise/ozone-wayland,shaochangbin/ozone-wayland,kishansheshagiri/ozone-wayland,mrunalk/ozone-wayland,clopez/ozone-wayland,01org/ozone-wayland,joone/ozone-wayland,siteshwar/ozone-wayland,Tarnyko/ozone-wayland