feat(hogql): nullish coalescing

[mariusandra]

Problem

Typing ifNull(bla, 0) everywhere is cumbersome. I'm used to so much better from TypeScript.

Changes

Adds ??, so instead of

select length(JSONExtractArrayRaw(ifNull(properties.$active_feature_flags, '[]'))) from events limit 1

you can do

select length(JSONExtractArrayRaw(properties.$active_feature_flags ?? '[]')) from events limit 1

How did you test this code?

I took care to have the operator precedence match what JS does. So 1 + null ?? 2 + 3 translates to (1 + null) ?? (2 + 3), and not 1 + (null ?? 2) + 3.

[Twixes]

This is nice