xwayland: add set_toplevel_with_position to internal API

Add a new entry to the internal interface between the xwayland plugin
and libweston-desktop (or any other desktop protocol implementation).
The new entry is identical to set_toplevel except it carries an absolute
position for the toplevel window.

Following patches will implement this new entry in
libweston-desktop and start using it in XWM.

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

xwayland/xwayland-internal-interface.h

@@ -38,6 +38,8 @@ struct weston_desktop_xwayland_interface {
 						      struct weston_surface *surface,
 						      const struct weston_xwayland_client_interface *client);
 	void (*set_toplevel)(struct weston_desktop_xwayland_surface *shsurf);
+	void (*set_toplevel_with_position)(struct weston_desktop_xwayland_surface *shsurf,
+					   int32_t x, int32_t y);
 	void (*set_parent)(struct weston_desktop_xwayland_surface *shsurf,
 			   struct weston_surface *parent);
 	void (*set_transient)(struct weston_desktop_xwayland_surface *shsurf,