[FLINK-12798][table-planner] Extracted the logic of converting from a Row type info to expected type

[dawidwys]

What is the purpose of the change

This PR extract the logic of converting from type info of the plan generated by optimizer to a given type. This further modularize the TableEnvironments and make it easier to port it.

Verifying this change

This change is already covered by existing tests.

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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[aljoscha]

I think this looks good now! I had some comments about outdated Javadoc that should be easy to fix. 👌

[aljoscha]

The javadocs on this are outdated.