Move result-to-array logic from SQL layer into QueryToolChests.

[gianm]

The main changes are the removal of query-result-to-array code from org.apache.druid.sql.calcite.rel.QueryMaker, and the addition of these two methods to QueryToolChest:

List<String> resultArrayFields(QueryType query);
Sequence<Object[]> resultsAsArrays(QueryType query, Sequence<ResultType> resultSequence);

I think this improves the design of the code a little bit, but the main benefit is really to support joins on subqueries. The change is needed by this item from the proposal #8728:

Allow joining on to "query" datasources as well. To make this work, we’ll need to add a sense of a ‘standard translation’ of results from certain query types into flat schemas that we can offer column selectors on top of. There may be more than one way to do this, since certain query types (notably, topN and scan) return nested results in some cases. We could do this by adding a new QueryToolChest method.

[clintropolis]

nit: should this be 'Returns a list of field names in the order that ...'

[gianm]

Yes, it should. I updated it. Thanks.

[clintropolis]

🤘