Refactoring AtomSet (part 2)

src/mol-data/int/map.ts

src/mol-data/util/equivalence-classes.ts

src/mol-data/util/hash-set.ts

src/mol-model/structure/_spec/atom-set.spec.ts

src/mol-model/structure/query/generators.ts

src/mol-model/structure/structure/atom/set.ts

src/mol-model/structure/structure/atom/set/builder.ts

src/mol-model/structure/structure/atom/set/impl.ts

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

src/perf-tests/structure.ts