Synch JSON-PP-4.18 into core

[jkeenan]

Changes since JSON-PP-4.16:

4.18 2026-03-20
    - fix duplicate specification warning (GH#93, 88; Heiko Jansen++)
    - fix typo (GH#92, sobrado8086++; GH#96, Grinnz++)
    - fix decode_json prototype (reported by bdfoy++)
    - fix space_after (GH#89, haukex++) 4.17_01 2023-07-29
    - fix a reentrant issue (experimental) (GH#61, 87)

Committer: Had to run ./perl -Ilib Porting/makemeta -j to get porting tests to pass.

NOTE: Given the point where we are in the perl-5.43/44 development cycle, I am placing this "synch-with-CPAN' product into a pull request rather than directly committing it to blead. Given that (a) we're past the "user-visible changes to correctly functioning programs" deadline, and (b) there have been a certain amount of code changes in the main JSON::PP module, I'm uncertain whether we should ship this with perl-5.44 or not. PSC: please advise. @ap @Leont @leonerd. Thanks.

[leonerd]

It's quite a big change. I'd certainly be tempted to say "not now" on the grounds that an equivalently-sized change on any of our core-first modules would not be permitted during this freeze time. But historically, "sync from CPAN" has always been somewhat of a backdoor process that we've occasionally allowed even very late in the freeze time anyway. So we have historic precedent in either direction on this one.

[jkeenan]

It's quite a big change. I'd certainly be tempted to say "not now" on the grounds that an equivalently-sized change on any of our core-first modules would not be permitted during this freeze time. But historically, "sync from CPAN" has always been somewhat of a backdoor process that we've occasionally allowed even very late in the freeze time anyway. So we have historic precedent in either direction on this one.

Thanks for the review. I'm going to mark it "defer-next-dev" because it's a very heavily used module and we have better things to do between now and the next dev release than to chase down all its revdeps.