xwayland: Include xwayland-window.h from xwayland-glamor-eglstream.c

Fixes build failure.

Closes: xorg/xserver#954
Fixes: 89e32d00 "xwayland: Move Xwayland windows to its own sources"
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Olivier Fourdan <ofourdan@redhat.com>
3 jobs for xwayland-eglstream-xwl_window in 13 minutes and 8 seconds (queued for 1 second)