This is really a defective redesign. It reintroduced numeric IDs to be removed by T114902.
See also T179928. We should reconsider reintroduce a new table to link unperfixed and
perfixed entity ID.
Also oppose any "partial migration for first XXX items" process in T221765: this
makes queries much more complicated. Please first fill all data in the new schema, then
discontinue the old table.