fix: order by m2m with disconnected records

[Weakky]

Overview

Fixes prisma/prisma#8036

Count aggregations on m2m were done from the join table and joined the relation tables. While this worked, it only returned records that had a count > 0.

SELECT A.id, COUNT(*) AS <AGGREGATOR_ALIAS> FROM _AtoB
  INNER JOIN A ON A.id = _AtoB.A
  INNER JOIN B ON B.id = _AtoB.B
GROUP BY A.id

This flawed the cursor logic, which needs to have all the records (the ones with a relation count > 0 and the ones without any connected records) to properly truncate the result set.

Instead of selecting from the join table (which contains only the connected records), we're now selecting from the base model and left joining the join table.

SELECT A.id, COUNT(_AtoB.B) AS <AGGREGATOR_ALIAS> FROM A
  LEFT JOIN _AtoB ON (A.id = _AtoB.B)
GROUP BY A.id