Equatable code for overriding == and hashcode

.dart

abstract class Equatable {
  /// {@macro equatable}
  const Equatable();
  
  ...
  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is Equatable &&
          runtimeType == other.runtimeType &&
          equals(props, other.props);

  @override
  int get hashCode => runtimeType.hashCode ^ mapPropsToHashCode(props);
  ...
}