gtk-shell: Work around non-working startup notifications

gtk-shell: Work around non-working startup notifications

GNOME Shell relies on the MetaScreen::startup-sequence-changed signal,
which is tied to (lib)startup-notification and therefore X11. As a result,
when we remove the startup sequence of a wayland client, GNOME Shell will
not be notified about this until startup-notification's timeout is hit.
As a temporary stop-gap, go through XWayland even for wayland clients,
so that the signal is emitted when expected.

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=768531
Applied-upstream: no

Gbp-Pq: Name bgo768531_workaround-startup-notifications.patch