No longer use it for internally-tagged enums. Instead, use a private helper that adds the tag property.

…ts`, regenerate test schemas

…n a schema's `properties`

This also changes the strategy for running visitors on subschemas - it is now done eagerly, as soon as they're added to the definitions map.

…efinitions` lazily (only if/when root schema is created).

Visitors will now always descend into `$defs`/`definitions`. If a generator is configured to use a different definitions path, then the visitor will also descend into that path (but a plain `Visitor` would NOT.