Java Binding: groupings should not share classes with their instantiations

Sharing classes between things encapsulated in a grouping fails on perfectly valid models which define leafrefs to instances known only at instantiation.

A typical example is https://github.com/openconfig/public/blob/master/release/models/bgp/openconfig-bgp.yang#L588, which is valid, but since the resulting target is not known within the grouping itself, DTO generation fails.

Resolving this problem clearly requires two interfaces being generated 'list neighbor': one for the grouping version, which will be just a DataObject (as nothing else is known about it) and a second one for the final instantiation place, where the type is already known to be inet:address.