chore(sql): fix subqueries returning a varchar column

[jerrinot]

Some SQLs with subqueries returning a varchar column were broken.

Example:

select * from outer where sym in (select varchar from sub where symbol = 'baz'),

The IN operator accepts a subquery returning a varchar column and this was broken.

Implementation note:
This bug was caused by some (delegating) RecordCursorFactories that expected inner Record to implicitly cast VARCHAR to STRING or SYMBOL. While Function performs such casting, Record does not. To complicate matters further, VirtualRecord appears to perform casting because it merely delegates to a function, which then handles the casting. This PR updates the affected CursorRecordFactories to explicitly convert VARCHAR columns to UTF-16 when necessary.

[jerrinot]

there are more cases to fix

[jerrinot]

it's ... not great. but doing this properly would require major changes. hopefully it will get simpler again once we start storing symbols as UTF8.

[bluestreak01]

@jerrinot could you rephrase PR title and add description. The existing title is very cryptic.

[ideoma]

[PR Coverage check]

😍 pass : 35 / 39 (89.74%)

file detail

	path	covered line	new line	coverage
🔵	io/questdb/cairo/sql/Record.java	7	11	63.64%
🔵	io/questdb/griffin/engine/table/FilterOnSubQueryRecordCursorFactory.java	2	2	100.00%
🔵	io/questdb/griffin/engine/table/LatestBySubQueryRecordCursorFactory.java	2	2	100.00%
🔵	io/questdb/griffin/engine/functions/bool/InSymbolCursorFunctionFactory.java	12	12	100.00%
🔵	io/questdb/griffin/SqlCodeGenerator.java	12	12	100.00%