[FLINK-37240][table] RowDataSerializer relaxes NOT NULL to NULL as a state compatibility change.

[Au-Miner]

What is the purpose of the change

RowDataSerializer relaxes NOT NULL to NULL as a state compatibility change.

Brief change log

• In RowDataSializer, extending the null value constraint of a field from NOT NULL to NULL is considered a state compatible schema change.

Verifying this change

This change is verified by new and existing tests in RowDataSerializerSnapshotTest.java.

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

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

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

[flinkbot]

CI report:

• d922445 Azure: SUCCESS

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