add JSON_QUERY_ARRAY function to pluck ARRAY<COMPLEX<json>> out of COMPLEX<json>

[clintropolis]

Description

This PR adds JSON_QUERY_ARRAY which is sort of like JSON_QUERY but instead of returning COMPLEX<json> for any value extracted from some json path, instead returns ARRAY<COMPLEX<json>>. This is currently done purely with ExpressionVirtualColumn via a DirectOperatorConversion rather than using the specialized NestedFieldVirtualColumn used by JSON_VALUE and JSON_QUERY, mostly because there isn't a lot of room for optimization yet, and I would rather wait until the future if we introduce specialized array column selectors than trying to extend the existing selectors of this virtual column to also handle arrays of objects.

Similar to other array handling, values which are not arrays will be coerced into single element arrays, though I am open to discussion on this, since it would seem equally valid to handle them as null values...

This allows for a lot of useful stuff like using UNNEST on arrays of objects, to transform an array of json objects into rows of json objects.

For example, using some data sourced from a discussion in a community slack thread, which has top level arrays of objects (would also work with nested arrays of objects at some path)

We can use JSON_QUERY_ARRAY to do stuff like translate it to a separate row per object:

and further use JSON_VALUE to extract values from these objects and do stuff like group or aggregate on them:

Will add docs in a follow-up PR.

Release note

Added JSON_QUERY_ARRAY which is similar to JSON_QUERY except the return type is always ARRAY<COMPLEX<json>> instead of COMPLEX<json>. Essentially, this function allows extracting arrays of objects from nested data and performing operations such as UNNEST, ARRAY_LENGTH, ARRAY_SLICE, or any other available ARRAY operations.

---

This PR has:

• been self-reviewed.
• added documentation for new or modified features or behaviors.
• a release note entry in the PR description.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• been tested in a test Druid cluster.

[clintropolis]

I imagine this function to be most useful actually with MSQ, to explode arrays of objects out into separate rows at ingest time, for example:

or even to extract values from the exploded objects into individual columns:

[abhishekagarwal87]

some minor comments. LGTM otherwise. Very useful capability.

[abhishekagarwal87]

we should add some validation on args count.

[abhishekagarwal87]

can you add a comment here as to why this is overridden?

[clintropolis]

oops, didn't mean to commit, was experimenting with CAST and forgot to remove this