wip, spacefill repr

src/apps/render-test/state.ts

src/apps/render-test/ui.tsx

src/mol-geo/primitive/polyhedron.ts

src/mol-geo/representation/structure/index.ts

src/mol-geo/representation/structure/spacefill.ts

src/mol-gl/attribute.ts

src/mol-gl/renderable/mesh.ts

src/mol-gl/shader/mesh.frag

src/mol-gl/shader/mesh.vert

src/mol-math/linear-algebra/3d.ts