[FLINK-38841][table] Enforce expected nullability in FamilyArgumentStrategy

[dylanhz]

What is the purpose of the change

Fix the issue where the nullability of the inferred data type is lost in FamilyArgumentStrategy.

Brief change log

• Enforce expected nullability in FamilyArgumentStrategy.
• Fix incorrect error message.

Verifying this change

• InputTypeStrategiesTest
• No built-in functions currently use FamilyArgumentStrategy with explicit nullability requirements, so this change has no impact on the existing public API.

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 documented)

[flinkbot]

CI report:

• c3426f2 Azure: SUCCESS

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[davidradl]

I think it would be useful for the issue text / PR text to give SQL examples of the reported issue and the expected behaviour - currently descriptions are very low level and require table planner knowledge. This would help users find and identify this issue at the SQL level