Rework VisibilityColumnConsideringSQLFilterTest

[janopae]

The VisibilityColumnConsideringSQLFilterTest is currently built as a heavy integration test, with a simulated Symfony Kernel and stuff. This on the one hand complicates the setup process - we need to simulate a request to get the filter activated. It also obscures the exact testing conditions, e.g. which FilterStrategy is used.

Also, working around the Doctrine caching could be solved by porting it to our webfactory/doctrine-orm-test-infrastructure.

Also, each test performing multiple assertions could be split.

Also, OneToOne-Relationships are currently only tested with EAGER-Loading - this detail is not visible from the Test case, but hidden in the test entity. Different tests for EAGER and LAZY for documenting the different effects the visibility filter has on each one of them would be helpful.