[lworld] RFR: 8281295: Prototype serialization/deserialization using Unsafe. [v2]

[Roger Riggs]

> Specify serialization and deserialization of value objects. Value objects are immutable, Externalizable relies on mutation, Externalizable is not supported for value objects. Revised tests and added tests for graphs of value objects.
> 
> Somewhat similar to Record serialization in that back references to the value object store 'null' until the value object is completely deserialized.
> Similar to regular serialization/deserialization of identity objects.  The serialized form is the same.
> Deserialization is done by reading fields and storing into a Buffered larval object, converted to a value object when all of the fields have been read and stored.
> 
> Externalizable and Value Objects are incompatible, value objects are immutable and Externalizable.readExternal is expected to modify the fields of an allocated object.

Roger Riggs has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - javadoc cleanup
 - Merge branch 'lworld' into 8281295-lworld-serialize
 - Merge branch 'lworld' into 8281295-lworld-serialize
 - 8281295: Prototype serialization/deserialization using Unsafe.
   
   Specify serialization and deserialization of value objects.
   Value objects are immutable, Externalizable relies on mutation,
   Externalizable is not supported for value objects.
   Revised tests and added tests for graphs of value objects.

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Changes: https://git.openjdk.org/valhalla/pull/761/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=761&range=01
  Stats: 1087 lines in 9 files changed: 787 ins; 287 del; 13 mod
  Patch: https://git.openjdk.org/valhalla/pull/761.diff
  Fetch: git fetch https://git.openjdk.org/valhalla pull/761/head:pull/761

PR: https://git.openjdk.org/valhalla/pull/761