[DO NOT MERGE] EZP-21906: integration tests for Field SortClause result filtering

JIRA: https://jira.ez.no/browse/EZP-21906

This PR attempts to exemplify the problem.
No actual tests fail, on the contrary: a `null` filter/query with a Field SortClause will return the exact same results as using `Criterion\ContentTypeId( 1 )`.

TODO: additional tests