Refactor EnumAnnotations and EnumFactory (#1747) (#1754)

This is a nit fix. no logic is changed.

* Rename `typeName` to `enumTypeName` in ScalaDoc
* Add return type at public method
* Rename `enum_records` into `enumRecords` to retain name consistency

Co-authored-by: Jack Koenig <koenig@sifive.com>
(cherry picked from commit 2a967670

)

Co-authored-by: SoyaOhnishi <ohnishi.soya@arc.cs.okayama-u.ac.jp>