status/keyboard: Preserve MRU order while IBus is disabled

status/keyboard: Preserve MRU order while IBus is disabled

In password fields, IBus sources are temporarily disabled and a backup
of the MRU list is created. If the user switches layouts in that state,
the active MRU list is updated, but the backup is not.

When IBus is enabled again, the stale backup is restored and the order
the user just selected is lost. Sync the backup on interactive source
switches while IBus is disabled, so the MRU order stays consistent.

Closes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/8538
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/4101>
(cherry picked from commit 8e0f850edc03ada8f79ef68412eabb05c5f76d02)