Update diagram codegen templates to support modeled diagram assistants:
- match visual-ID hinted types by subtype in the view providers instead of matching
on exact element types
- match visual-ID hinted types by subtype in looking up target compartment for
- make creation of GEF wrappers for edit commands null-safe
Regenerate Use Case and Class diagrams. Generate and customize Diagram Assistant
models for Use Case and Class diagrams and integrate them.