[sdfui] Add collaborative design illustration/free-form drawing

**The task** Free form drawing to aid thinking and communicating to subordinates about abstract forms, perhaps with little or no respect to context or constructability. Often this involves providing feedback to designers on an ad-hoc basis. **Frequency of this task** For competitions and projects with high demands on the design, a single design partner can conduct these meetings 1-2 times a day for up to an hour each session. **Story of the task** A busy design partner has a free hour in the middle of the day to review the work of 3-10 designers. They haven't prepared design materials but take screenshots of their models that the design partner sketches over. The design partner quickly draws with gestural strokes to evoke an idea of a form or arrangement of forms to the designers. They may raise questions or concerns about ideas, but it is generally taboo for them to draw on the partner's work. They may apply a layer of trace or start another drawing to communicate their idea.