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.