use FilterProviderInterface

The `FilterProviderInterface` is referenced twice in the `DoctrineObject` class however that class does not exist in the `DoctrineModule\Stdlib\Hydrator` namespace. I'm assuming the `use` statement was omitted accidentally as `instanceof` will not catch nonexistent classes.


This is a duplicate of #408 however I've attempted to add unit tests to help get this in sooner rather than later.