Updated specifications

[Dan Smith]

I've posted updated specifications for JEP 401 here:

https://cr.openjdk.org/~dlsmith/jep401/jep401-20240603/specs/value-objects-jls.html
https://cr.openjdk.org/~dlsmith/jep401/jep401-20240603/specs/value-objects-jvms.html

These are intended to address all the needs of JEP 401, and I don't expect many further revisions—but as always, happy to hear any feedback.