Updating TranslationKeyFragment conversion

Instead of relying on the objects work type, instead rely on the
presented object. After all the presented object may very well
implement a #to_translation_key_fragment method which very likely
delegates to the object's #work_type
Removing forced presentation structure

Given that the spec is generating what passes as a presentation
structure, I'll lean on that instead of hand crafting my own.
Adding test for WorkType() conversion

I was not testing a thing that was not empty?