lookup3d at structure level, color provider

src/mol-model/structure/structure/accessible-surface-area.ts

src/mol-model/structure/structure/unit.ts

...ructure/structure/unit/accessible-surface-area/compute.ts

.../structure/structure/unit/accessible-surface-area/data.ts

src/mol-model/structure/structure/util/lookup3d.ts

src/mol-theme/color.ts

src/mol-theme/color/accessible-surface-area.ts

src/tests/browser/render-structure.ts