An arbitrary polygon on the ground plane, extruded between minZ and
maxZ.
Use this when no primitive fits: a police station's grounds, a race track sector, a gang territory that follows the streets. Trace the outline as a list of points in order (either winding direction works) — the shape closes itself, so don't repeat the first point at the end.
Containment is a standard ray-crossing test, which is exact for both convex
and concave outlines. It costs one comparison pass per vertex, so the
inherited boundingRadius rejection matters more here than for the
primitive shapes.