Features
- spanner/spannertest: implement RowDeletionPolicy in spannertest (#4961) (7800a33), refs #4782
- spanner/spannertest: Support generated columns (#4742) (324d11d)
- spanner/spansql: fill in missing hash functions (#4808) (37ee2d9)
- spanner/spansql: support JSON data type (#4959) (e84e408)
- spanner/spansql: Support multiple joins in query (#4743) (81a308e)