BufferPrimitiveCollection: Sandcastle visual comparisons

It'd be very helpful to have a Sandcastle comparing BufferPoint/Polyline/Polygon classes to existing CesiumJS APIs for points/lines/polygons. Goal is to verify that interpretation and rendering of properties like "size" and "width" are consistent, pixel alignment, aliasing, etc. Probably easiest to see with a small number of fairly simple shapes, at varying scales.

Start with the existing Sandcastle examples and the BufferPoint, BufferPolyline, and BufferPolygon APIs, then compare them with the corresponding CesiumJS point, line, and polygon APIs. Use a small set of simple shapes at varying scales and inspect size, width, pixel alignment, and aliasing. Done means the Sandcastle provides clear visual comparisons of these properties.

Written by the indexing model from the issue text.