xdg-shell: upgrade to support current version (weston-1.5.0)

The protocol file is a raw copy of

Source: http://cgit.freedesktop.org/wayland/weston/plain/protocol/xdg-shell.xml?id=1.5.0

Task-number: QTBUG-38633/related
Change-Id: I41ca2f89c09a8b6348ce2fbf6d59f44b4c8134df
Reviewed-by: Giulio Camuffo <giulio.camuffo@jollamobile.com>
Reviewed-by: Philippe Coval <rzr@gna.org>