ElementImpl#getOwnedAnnotation doesn't work as expected

[gdaniel]

This seems to be related to filter(annotation -> this.equals(annotation.getAnnotatedElement())), where annotation.getAnnotatedElement always returns null.
To retrieve all the annotations of an element, one should still iterate over Element#getOwnedRelationship() instead of getOwnedAnnotation.

This change has been introduced in #2034

This issue seems to be linked to an ongoing issue in the KerML specification.