Notify update listeners once view compaction finishes

Due to view compaction retries, it's possible the compacted
group has caught up with the updater's group and it's actually
more recent that the view group's current group snapshot.
In this case notify the update listeners, as a new index update
might not be triggered until new changes are applied to the
vbucket databases and a subsequent query with stale=false or
stale=update_after arrives.