RFR: 8333796: Add missing serialization functionality to sun.reflect.ReflectionFactory [v6]

[David M. Lloyd]

> Issue [JDK-8164908](https://bugs.openjdk.org/browse/JDK-8164908) added support for functionality required to continue to support IIOP and custom serializers in light of additional module-based restrictions on reflection. It was expected that these libraries would use `sun.misc.Unsafe` in order to access fields of serializable classes. However, with JEP 471, the methods necessary to do this are being removed.
> 
> To allow these libraries to continue to function, it is proposed to add two methods to `sun.reflect.ReflectionFactory` which will allow serialization libraries to acquire a method handle to generated `readObject`/`writeObject` methods which set or get the fields of the serializable class using the serialization `GetField`/`PutField` mechanism. These generated methods should be used by serialization libraries to serialize and deserialize classes which do not have a `readObject`/`writeObject` method or which use `ObjectInputStream.defaultReadObject`/`ObjectOutputStream.defaultWriteObject` to supplement default serialization.
> 
> It is also proposed to add methods which allow for the reading of serialization-specific private static final fields from classes which have them.
> 
> With the addition of these methods, serialization libraries no longer need to rely on `Unsafe` for serialization/deserialization activities.
> cc: @AlanBateman

David M. Lloyd has updated the pull request incrementally with one additional commit since the last revision:

  Address review feedback

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Changes:
  - all: https://git.openjdk.org/jdk/pull/19702/files
  - new: https://git.openjdk.org/jdk/pull/19702/files/34d45238..38f7b79a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19702&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19702&range=04-05

  Stats: 30 lines in 2 files changed: 7 ins; 3 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/19702.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19702/head:pull/19702

PR: https://git.openjdk.org/jdk/pull/19702