intersection method
As Set.intersection but takes a BuiltSet<Object?> and returns a
BuiltSet<E>.
Implementation
BuiltSet<E> intersection(BuiltSet<Object?> other) =>
    _BuiltSet<E>.withSafeSet(_setFactory, _set.intersection(other._set));As Set.intersection but takes a BuiltSet<Object?> and returns a
BuiltSet<E>.
BuiltSet<E> intersection(BuiltSet<Object?> other) =>
    _BuiltSet<E>.withSafeSet(_setFactory, _set.intersection(other._set));