DBAL-968

The recent change to SQLServerPlatform.php (https://github.com/doctrine/dbal/commit/17dad30dc9acd91a5cda0da2c5ce2c40d522f766) broke the ORM Paginator's queries on SQL server.

I investigated, and found that some of the test cases for the SQL Server platform weren't actually correct SQL. Also, there were no test cases that covered what the paginator is doing, so I've written test cases for those. I will open a pull request for this issue.

The modifyLimitQuery method in SQLServerPlatform.php should be fixed to pass the fixed old tests and the new tests.

My concern is that that method is becoming too complex, but that's an issue for another day.
should be ``@param string $sql``