- Split Edge, Extend Edge and Extend Vertex have been migrated to a new module
- Added support for extensible mesh commands that drag mesh elements immediately after an action
- Fixed selection undo events added with empty selection sets
- Simplified extensibility API for mesh commands that apply during a drag
#codereview richard.talbotwatkin
#rb none
[CL 3372877 by Mike Fricker in Dev-Geometry branch]
