[FLINK-35864][table] Add CONV function

[dylanhz]

What is the purpose of the change

Add CONV function. Examples:

> SELECT CONV(7, 10, 2);
111

Brief change log

FLINK-35864

This implementation is inspired by Spark.

Verifying this change

MathFunctionsITCase#convTestCases

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): (yes)
• 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? (yes)
• If yes, how is the feature documented? (docs)

[flinkbot]

CI report:

• f915a7a080665019b6dff747c097b0e281472693 Azure: SUCCESS

Bot commands

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[github-actions[bot]]

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[github-actions[bot]]

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