[FLINK-16301][table-api] Improve logging message in ModuleManager

[wuchong]

What is the purpose of the change

The unknown functions in ModuleManager is logged in INFO level which is very verbose and useless for users.

Brief change log

• Change the log level to DEBUG for unknown functions. (maybe we can even remove it)
• Improve the messages to make the function name and module name more obvious.

Verifying this change

This change added a test which transforms a nested data type.

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, Yarn/Mesos, 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)

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Automated Checks

Last check on commit fb2f9e1 (Thu Feb 27 14:13:24 UTC 2020)

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CI report:

• fb2f9e1 Travis: SUCCESS

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