find method
Fast lookup for a RealmObject of type className with the specified primaryKey.
Implementation
RealmObject? find(String className, Object primaryKey) {
  final metadata = _realm._metadata.getByName(className);
  final handle = _realm.handle.find(metadata.classKey, primaryKey);
  if (handle == null) {
    return null;
  }
  final accessor = RealmCoreAccessor(metadata, _realm._isInMigration);
  return RealmObjectInternal.create(RealmObject, _realm, handle, accessor) as RealmObject;
}