[FLINK-21912][pyflink] Introduce ResolvedSchema in Python Table API

[autophagy]

What is the purpose of the change

Currently, ResolvedSchema is not supported in the Python Table API. This PR introduces it, as well as adding get_resolved_schema() to Table and replaces get_table_schema() in TableResult with get_resolved_schema(), similar to ba5b122.

Brief change log

• ResolvedSchema is introduced to Python Table API.
• Table.get_resolved_schema() is added.
• TableResult.get_table_schema() is replaced by TableResult.get_resolved_schema()

Verifying this change

Please make sure both new and modified tests in this PR follow the conventions for tests defined in our code quality guide.

• This change is already covered by existing tests, such as sql and table environment api tests.
• This change adds a test to the schema operation tests to verify the returned resolved schema is as expected.

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 (in the sense that it changes the public api of TableResult and Table))
• 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:

• a6913cc Azure: SUCCESS

Bot commands

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• @flinkbot run azure re-run the last Azure build

[autophagy]

I missed some docs updates, will turn this PR back to draft until i've updated them.

[davidradl]

nit: I am not sure how to read this sentence, what do we mean by original here? and what might be expected to be different around time attributes.

[autophagy]

I am not entirely sure what is meant, the docs for this class were just pulled from the Java equivalent https://nightlies.apache.org/flink/flink-docs-stable/api/java/org/apache/flink/table/catalog/Column.html - perhaps it's not necessary to include this in the Python one, since it doesn't really 'enclose' the data type like the Java one does.