Revised JVMS changes for JEP 401

[Dan Smith]

FYI, I've posted an update to the JEP 401 JVMS changes:

https://cr.openjdk.org/~dlsmith/jep401/jep401-20240503/specs/value-objects-jvms.html

Addresses a variety of small issues raised in the last few months.

One notable change is the use of a new exception type, IdentityException, to indicate misuse of value objects, including attempted 'monitorenter' and 'monitorexit'.

Another is to clarify the ways in which Preload can be used, at the discretion of implementations.

(Still to investigate: ideas about alternative encodings for the Preload attribute.)