[FLINK-39672][docs] Document Java records as supported POJO types

[liuml07]

What is the purpose of the change

This backports PR #28149 to release-1.20 for FLINK-39672

Adapted for release-1.20: drop the older one-liner about Java records introduced in 10157ff, which is now superseded by the more detailed POJO-types description added by this commit.

Java records have been supported as POJO types since Flink 1.19 (FLINK-32380), but the only doc mention lived on the release-1.20 java_compatibility page and was inadvertently removed on master by FLINK-37339.

Brief change log

• Restores the FLINK-32380 reference under "Java 17" in java_compatibility.md and notes that records are handled as POJO types serialized via their canonical constructor.
• Adds a note in both POJO listings in types_serialization.md that a public record class is serialized by PojoSerializer; the no-argument constructor and getter/setter requirements do not apply.
• Mentions in schema_evolution.md that records follow the same POJO schema evolution rules.

Parallel updates in docs/content.zh.

Verifying this change

Doc-only change.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

---

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Generated-by: Claude Opus 4.7

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CI report:

• 37bfe2a Azure: FAILURE

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[snuyanzin]

@liuml07 instead of having AI as a co-author can you changed it to generated by as mentioned at
https://github.com/apache/flink/blame/1e6a73616eb4e224a149e684c832f20bcba93148/AGENTS.md#L327

[liuml07]

Thanks @snuyanzin I have addressed that.

A quick question is in old branches which are still active (<=release-2.2) There is no AGENTS.md file there. Isn't it better to have that as well so when working with backports, agents can find and honor the same AGENTS.md

[snuyanzin]

A quick question is in old branches which are still active (<=release-2.2) There is no AGENTS.md file there. Isn't it better to have that as well so when working with backports, agents can find and honor the same AGENTS.md

yes makes sense to backport to branches
feel free to create backport PRs

[liuml07]

@snuyanzin Thanks for the reply. I have filed pull requests for the new backport JIRA FLINK-39714 Each PR has two commits: one faithful copy from master branch, and the other adapt for the release branch (e.g. update modules / files mentioned that are non-existent)