RFR: JDK-8312415: Expand -Xlint:serial checks to enum constants with specialized class bodies [v2]

[Joe Darcy]

> Thanks to @lahodaj for providing the code to bridge into the class used for a enum constant with a specialized body.
> 
> This changes expands serialization warnings to the contents of any such class bodies.

Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:

  Respond to review feedback.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15004/files
  - new: https://git.openjdk.org/jdk/pull/15004/files/d61f9114..d659d7f4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15004&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15004&range=00-01

  Stats: 7 lines in 1 file changed: 1 ins; 2 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/15004.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15004/head:pull/15004

PR: https://git.openjdk.org/jdk/pull/15004