Support for `record`

With the release of Java 16 in March 2021 the broad use of the `record` keyword is expected to grow.

I'd like to propose that the JAXB API clearly defines if and how the `record` keyword is supported by JAXB:
* Can records be used with JAXB?
* How to annotate records, as most methods and fields no exists unless overwritten?
* Are there benefits / drawbacks of using records over custom classes in *direct* relation to JAXB?
* Is support for records *mandatory* for implementations of the JAXB API (hence, is it safe to be used by vendor-agnositic applications)?

No source files or tests are named. Start by reviewing the JAXB API specification and its Java 16 record support requirements; determine whether records are supported, how they can be annotated, and whether implementations must provide support. Done means the API's requirements and compatibility guidance are clearly defined.

Written by the indexing model from the issue text.