[FLINK-32721][table-planner] Fix SQL MAX aggregation function does no…

[paul8263]

…t support CHAR type

What is the purpose of the change

Support max aggregation with char data type by reusing the existing MaxAggFunction.

Brief change log

Files updated:

• flink-table/flink-table-planner/src/main/scala/org/apache/flink/table/planner/plan/utils/AggFunctionFactory.scala

Verifying this change

This change is covered in existing unit test and manual test. Please see also FLINK-32721

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:

• 84c306d Azure: SUCCESS

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[lsyldliu]

@paul8263 Thanks for your contribution, this will be fixed by #18375, this pr will be closed later.