improved carbohydrate/anomeric carbon picking/loci

src/mol-model/structure/structure/carbohydrates/compute.ts

src/mol-model/structure/structure/carbohydrates/data.ts

src/mol-repr/structure/visual/carbohydrate-symbol-mesh.ts

src/mol-repr/structure/visual/util/common.ts

src/mol-theme/color/carbohydrate-symbol.ts