[FLINK-37695][table] Fix parsing for built-in function JSON in JSON_OBJECT for all positions

[gustavodemorais]

What is the purpose of the change

Parsing for a JSON() function call fails if its position is not the first param of JSON_OBJECT.

SELECT JSON_OBJECT('key' VALUE JSON('{}'), 'key_2' VALUE JSON('{}'));

Outputs:

The JSON() function is currently only supported inside a JSON_OBJECT() or JSON_ARRAY() function. Example: JSON_OBJECT('a', JSON('{\"key\": \"value\"}')) or JSON_ARRAY(JSON('{\"key\": \"value\"}'))

This is incorrect, we were too strict with the limitations. We're strictly allowing json to be called only as the second param in the function, when it should be allowed for every second.

Brief change log

(for example:)

• Check if the JSON call is for any of the VALUES param inside a JSON_OBJECT and not only the first one

Verifying this change

This change added tests and can be verified as follows:

• Added unit tests

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? (already covered by docs / JavaDocs)

[flinkbot]

CI report:

• 199815d Azure: SUCCESS

Bot commands

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[lihaosky]

The error message is confusing though. JSON() function is indeed inside JSON_OBJECT. We need to make it more accurate that it also needs to be in value position?

[gustavodemorais]

The full message contains examples that should help the user understand the expected use. See:

The JSON() function is currently only supported inside a JSON_OBJECT() or JSON_ARRAY()" +
          " function. Example: JSON_OBJECT('a', JSON('{"key": "value"}')) or " +
          "JSON_ARRAY(JSON('{"key": "value"}')).

Do you think that's clear enough? Let me know if you have a specific suggestion

[lihaosky]

The JSON() function is currently only supported inside a JSON_OBJECT() or JSON_ARRAY() as values? Is this more accurate?

[gustavodemorais]

The param is actually called VALUE. What do you think:

The JSON() function is currently only supported inside JSON_ARRAY() or as the VALUE param of JSON_OBJECT()

[snuyanzin]

Thanks @gustavodemorais for the contribution
Thanks @lihaosky for the review