Add link-time support for automatic modules

We may need to support linking automatic modules into the run-time image. At this time, then jlink will fail if a modular JAR does not contain a module-info.class.

One approach is to write the ModuleDescriptor as a module-info.class when creating the image, this is easy to do. The awkward part is detecting it as an automatic module as run-time so that the appropriate read edges can be set and the module changed to loose. This is could be done with a special internal flag on the module.