programming model for converters and listeners

The spec does not say that:

1. entity listener classes must be non-abstract, nor
2. whether they must be `public`.

It does say that they must have a public no-args constructor. I doubt this is even correct when they're instantiated via CDI.

Even worse, the spec does not say much at all about converters:

1. it doesn't mention they can't be abstract,
2. it doesn't say anything about constructors,
3. it doesn't mention anything about visibility.

We should clear all this up.

Start by reviewing the Persistence specification sections covering entity listeners, converters, constructors, visibility, and CDI instantiation. Compare the current rules for both types and document whether they may be abstract, required visibility, and constructor requirements; done means these questions are explicitly and consistently resolved in the specification.

Written by the indexing model from the issue text.