debugKnownRoutes method
Returns the full path of routes.
Each path is indented based depth of the hierarchy, and its name
is also appended if not null
Implementation
@visibleForTesting
String debugKnownRoutes() {
  final StringBuffer sb = StringBuffer();
  sb.writeln('Full paths for routes:');
  _debugFullPathsFor(
      _routingConfig.value.routes, '', const <_DecorationType>[], sb);
  if (_nameToPath.isNotEmpty) {
    sb.writeln('known full paths for route names:');
    for (final MapEntry<String, String> e in _nameToPath.entries) {
      sb.writeln('  ${e.key} => ${e.value}');
    }
  }
  return sb.toString();
}