Adapter class loaders can avoid creating named dynamic modules

Adapter classes are generated into named dynamic modules. The only package in those modules are exported. The adapter class generated in an adapter named module is exported as well (adapter is a subtype of public/exported supertypes).

Given that nashorn does not allow subclassing/implementing

* package-private classes, interfaces
* or types in non-exported packages of modules

we can simplify code by using the default unnamed module of the adapter class loader. Nashorn module can still selectively export packages to adapter's (unnamed) module. This also avoids having to generate a class that will "module read" links to the reference types used in adapter!