Java compilation units [JLS14:7.3].
This is a product type introduced by fty::defprod.
We only capture ordinary compilation units, not modular ones. Thus, we do not capture module declarations either.
We capture the package declaration [JLS14:7.4] as an ACL2 string for the name. This declaration is optional.
We do not capture interfaces, so a type declaration [JLS14:7.6] is always a class declaration.