fix(pagination): fix bug in cursor pagination for PL/pgSQL SETOF functions

[benjie]

Fixes graphile/crystal#1171

useAsterisk runs certain code in a subquery as an optimisation; so:

select /* COMPLEX STUFF */
from /* EXPENSIVE THING */
limit 2 offset 2

becomes

select /* COMPLEX STUFF */
from (
  select *
  from /* EXPENSIVE THING */
  limit 2 offset 2
) as __alias__

This is great because it means that PostgreSQL can process the rows in the subquery more efficiently, and doesn't have to execute the "COMPLEX STUFF" until it's thrown most of the rows from "EXPENSIVE THING" away. Less computation = faster queries (even though they're a little more complex).

HOWEVER because we've moved the LIMIT/OFFSET to the subquery, any calls to row_number() are now different than they were before because they no longer include the OFFSET. In this code, we add it back in. It's kinda hacky, but it's a performance optimisation so we're just going to have to suck it up 😉