RFR: JDK-8310835: Address gaps in -Xlint:serial checks [v2]

[Joe Darcy]

On Fri, 14 Jul 2023 16:42:30 GMT, Joe Darcy <darcy at openjdk.org> wrote:

>> Improve serial lint messages for externalizable records (and potentially other situations).
>
> Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix typo found in code review.

After some one-off checking with a small test program, I verified the implementation does _not_ call readExternal or writeExternal on an Externalizable enum. I'll update the messages accordingly.

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PR Comment: https://git.openjdk.org/jdk/pull/14639#issuecomment-1636518761