wip, repr instancing support

src/apps/render-test/state.ts

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

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

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

src/mol-gl/renderable/point.ts

src/mol-gl/renderer.ts

src/mol-gl/shader/point.vert