mol-canvas/gl: refactored scene add/remove object sync

src/mol-canvas3d/canvas3d.ts

src/mol-gl/_spec/renderer.spec.ts

src/mol-gl/scene.ts

src/mol-plugin/behavior/static/camera.ts

src/mol-plugin/behavior/static/representation.ts

src/tests/browser/marching-cubes.ts

src/tests/browser/render-lines.ts

src/tests/browser/render-mesh.ts

src/tests/browser/render-shape.ts

src/tests/browser/render-spheres.ts

src/tests/browser/render-structure.ts

src/tests/browser/render-text.ts