Paginator: Skip limit subquery if not required

[Seb33300]

This fixes #7829

[SenseException]

@lcobucci Are these $query->setMaxResults(1); in the older tests not an indicator for a breaking change that needs to target master?

[Seb33300]

I feel more like I fixed issues in older tests.

They are both related to the Paginator and tests was failing because they was expecting the Limit Subquery to be applied, but without adding a LIMIT to the query...
And an empty limit will return all data, so this is why my PR is intended to skip the limit query in this case. So only 2 queries will be executed instead of 3.

The only BC that could happen is if you use the SQLLogger to count how many queries have been executed when using a Paginator without LIMIT, like in the failing test:

$this->connection->expects($this->exactly(3))->method('executeQuery');

[lcobucci]

@Seb33300 there's a small change which is not BC compatible here as highlighted by @SenseException: no length + usage of output walkers. But then again, the output walker is useful when performing the subquery.

[lcobucci]

@Seb33300 🚢

I marked this with BC Break because behaviour might change a tiny bit. I just forgot to document it in UPGRADE.me, will do it separately. Thanks for your contribution.