[util] reggen enhancement for enums

Enhance reggen such that it can automatically create enums when a particular field is defined that way.
This will prevent the designer from needing to create a second version inside a package file somewhere, and will also ensure the documentation and the design stay in sync.

Start by locating the reggen utility and how field definitions are represented. Trace where package-file enums and generated documentation are currently handled, then determine the expected enum-generation behavior. Done means reggen creates enums from fields defined that way without requiring a second package-file version, keeping documentation and design synchronized.

Written by the indexing model from the issue text.