Add ComparatorUtils

[AndreTheHunter]

class ComparatorUtils {
  ComparatorUtils._();

  static Comparator<T> compareBy<T, C extends Comparable<C>>(
    C Function(T) selector,
  ) {
    //based on https://pub.dev/documentation/kt_dart/latest/kt_collection/compareBy.html
    return (T a, T b) => selector(a).compareTo(selector(b));
  }

  static Comparator<T> compareByDescending<T, C extends Comparable<C>>(
    C Function(T) selector,
  ) {
    //based on https://pub.dev/documentation/kt_dart/latest/kt_collection/compareByDescending.html
    return (T a, T b) => selector(b).compareTo(selector(a));
  }
}