Creates an insertion-ordered identity-based set.
Effectively a shorthand for:
new LinkedHashSet<E>(equals: identical,
                     hashCode: identityHashCode)   external factory LinkedHashSet.identity();
    © 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
    https://api.dart.dev/stable/2.5.0/dart-collection/LinkedHashSet/LinkedHashSet.identity.html