speed up

Fixed

csg.js

• Vertex.normal is now optional

Refactor

meshToPolygons()

• Attach Material directly to CSG.Polygon shared data instead of (mesh.material, materialIndex) tuple
• Eliminated many consts during construct-CSG.Polygon-loop

csgToMesh()

• Use truthy/falsy checking instead.. for probing existence of attributes.normal etc.
• Use uvs[i++] = ... instead of uvs.set(uv.toArray(), i)