new tool - xisxwayland

[Peter Hutterer]

Hi all,

I'm planning to move this little tool to the xorg/app folder, but I'd like
to double-check that we don't already have something like this:
https://gitlab.freedesktop.org/whot/xisxwayland/

it's a tiny C program that connects to the X server and exits with status 0
if the X server is Xwayland, or 1 otherwise. To be used in shell scripts,
modeled after the selinuxenabled command:

    if xisxwayland; then
       echo "don't bother runing xinput, you're on wayland"
    fi

It currently uses RandR output names to check but if that ever changes, we
can change this accordingly.

Cheers,
   Peter