dump method
Creates a readable dump from the current ASN1Object.
Important note: Subclasses need to override this method. If the ASN1Object is constructed and has child elements, dump() has to be called for each child element.
Implementation
@override
String dump({int spaces = 0}) {
  var sb = StringBuffer();
  for (var i = 0; i < spaces; i++) {
    sb.write(' ');
  }
  sb.write('SEQUENCE (${elements!.length} elem)');
  for (var e in elements!) {
    var dump = e.dump(spaces: spaces + dumpIndent);
    sb.write('\n$dump');
  }
  return sb.toString();
}