unorderedEqualItems method
Will return true
only if the ISet and the iterable items have the same number of elements,
and the elements of the ISet can be paired with the elements of the iterable, so that each
pair is equal. This may be slow for very large sets, since it compares each item,
one by one.
Implementation
bool unorderedEqualItems(covariant Iterable? other) {
if (other == null) return false;
if (identical(this, other) || (other is ISet<T> && same(other))) return true;
return const UnorderedIterableEquality<dynamic>().equals(_s, other);
}