Rendering the strokes of vector meshes

Vector meshes generalize paths to have more than two edges connected to a point. That messes with assumptions made by the renderer as part of stroking for caps and joins. We need to devise a strategy for properly rendering such cases.

It would also potentially be worthwhile to control the caps and joins (and miter limit) on a per segment or per anchor basis, even at both ends of just a simple line.

This is currently handled badly, as we can see from the line caps:


Start in the renderer's stroking path, focusing on cap and join handling for vector meshes and the assumptions around points with more than two connected edges. Define and validate a strategy for correctly rendering these cases; per-segment or per-anchor cap, join, and miter-limit controls are noted as a possible extension.

Written by the indexing model from the issue text.