[FLINK-34111][table] Add support for json_quote, json_unquote, address PR feedback #24156

[anupamaggarwal]

What is the purpose of the change

Adds implementation of json_quote and json_unquote functions.
PR is a continuation of #24156 and addresses feedback received on the original PR.

Brief change log / changes compared to PR 24156

• Update implementation for json_quote with escaping logic
• Update implementation for json_unquote to unescape special characters
  • Delegates valid json checking to SqlJsonUtils#isJsonValue
• Add/ update some additional tests
• Updates documentation to remove reference to MySql utf8mb4 encoding

Open questions

• High level behavior for invalid json in json_unquote (pass original input as is, Vs throwing exception)
• To check for JSON_VALIDITY for json_unquote logic for IS JSON is used but in certain cases IS JSON behaviour does not seem to be consistent with Json spec as documented here https://www.json.org/json-en.html
  • According to json spec """" should not be a valid json (which is also flagged by JsonLint) but select '""""' IS JSON returns true
    • In case of invalid json string for json_unquote an exception is thrown in case of Mysql (However we won't do the same)

References

• postgres implementation for escape

Verifying this change

• Added ITs in JsonFunctionsITCase

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

[flinkbot]

CI report:

• 48b570f Azure: SUCCESS

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[anupamaggarwal]

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