[lworld] Follow up tasks to JDK-8237072

This is a laundry list of known problems deferred from JDK-8237072 to the next iteration:

 - With consent from Brian, the translation strategy employed at JDK-8237072 is a simpler scheme than what is described in https://cr.openjdk.java.net/~briangoetz/valhalla/sov/04-translation.html In particular, the members sorting algorithm outlined the document is not opted to, but we use a scheme that would yield compatible and correct behavior for val-default classes. But in order to enable migration of VBC's we should enhance the translation scheme.
 - ref-default and val-default "keywords" are not accepted yet and all value classes are value default and non-nullable as of now.
 - V$ref.class and V.class are supposed to be nest mates - this is only half heartedly attempted as of now. In particular we don't generate the NESTHOST attribute
- No support for sealing of the hierarchy between V$ref.class and V.class