uv3: DocumentAnnotation subclasses not handled as in UIMAv2 during deserialization

Consider the case that you have custom subclass of the uima `DocumentAnnotation`, let's call it `DocumentMetaData`. Next, we have an XMI file which contains an annotation of the `DocumentMetaData` type.

When loading such an XMI file in UIMAv2, the CAS ends up with a single `DocumentMetaData` annotation which is accessible via `cas.getDocumentAnnotation()`.

When loading the same file with UIMAv3, the CAS ends up with both, a `DocumentAnnotation` and a `DocumentMetaData` annotation and `cas.getDocumentAnnotation()` returns the former.

The same appears to happen when deserializing a CAS from various binary formats.