[FLINK-37923][sql] Introduce VARIANT type and PARSE_JSON to Flink SQL

[Sxnan]

What is the purpose of the change

This pull request introduces the Variant data structure to represent semi-structured data, a new SQL type variant, and a builtin method to parse json string to the variant type.

Brief change log

• Patch calcite to support variant type
• Introduce Variant and BinaryVariant
• Introduce variant type and PARSE_JSON to Flink SQL

Verifying this change

This change added tests and can be verified.

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
• 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? JavaDocs

[flinkbot]

CI report:

• 9513d8eeb67c4b79c2b93437933a28a0630807f3 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

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

[Sxnan]

@twalthr Thanks for the detailed review! I updated the PR accordingly, and all the comments should be addressed. Please take another look.

[twalthr]

Thanks @Sxnan. I added it for my list for tomorrow. I'm sure it can still make it before the feature freeze.

[Sxnan]

Hi @twalthr, could you take another look at your earliest convenience, in case we need to make some final adjustment to the PR before the feature freeze tomorrow.

[Sxnan]

Hi @twalthr, thanks for the review! I updated the PR accordingly in the last two fixup commits. Please take another look.

[Sxnan]

Fixup commits are squashed. Will merge after the test passes.

[Sxnan]

@gustavodemorais Yes, it will be covered later in another PR.