added graphics and compute render item variants

src/mol-canvas3d/canvas3d.ts

src/mol-gl/renderable.ts

src/mol-gl/renderable/direct-volume.ts

src/mol-gl/renderable/lines.ts

src/mol-gl/renderable/mesh.ts

src/mol-gl/renderable/points.ts

src/mol-gl/renderable/spheres.ts

src/mol-gl/renderable/text.ts

src/mol-gl/renderer.ts

src/mol-gl/webgl/render-item.ts