Auto-generate stable fixture UUIDs on PostgreSQL.
Fixes: #11524
Optionally support the `uuidtools` gem for faster UUID fixture generation.
Add uuid_v3 and uuid_v5 methods to SecureRandom to remove uuidtools dependency.
Fix handling of timestamp and datetime columns on PostgreSQL.

Timestamp columns are defined as `timestamp with time zone`,
datetime columns as `timestamp without time zone`. PostgreSQL
converts timestamp values from the local time zone to UTC for
storage and back; datetime values are treated as-is. This is in
line with MySQL.
Optionally support the `uuidtools` gem for faster UUID fixture generation.
Auto-generate stable fixture UUIDs on PostgreSQL.
Fixes: #11524
Optionally support the `uuidtools` gem for faster UUID fixture generation.
Add uuid_v3 and uuid_v5 methods to SecureRandom to remove uuidtools dependency.
Clean up primary_key_type API.