message: Don't use get_shared_realm() in the place where we can't use get_shared_realm()
diff: @@ -276,12 +276,15 @@ void SyncMetadataManager::make_file_action_metadata(StringData original_name,
  // This function can't use get_shared_realm() because it's called on a
  // background thread and that's currently not supported by the libuv
  // implementation of EventLoopSignal
  - std::unique_ptr<Group> read_only_group;
  - auto realm = _impl::RealmCoordinator::get_coordinator(m_metadata_config)->get_realm();
  - realm->begin_transaction();
  + auto coordinator = _impl::RealmCoordinator::get_coordinator(m_metadata_config);
  + auto group_ptr = coordinator->begin_read();
  + auto& group = *group_ptr;
  + REALM_ASSERT(typeid(group) == typeid(Transaction));
  + auto& transaction = static_cast<Transaction&>(group);
  + transaction.promote_to_write();
  // Retrieve or create the row for this object.
  - TableRef table = ObjectStore::table_for_object_type(realm->read_group(), c_sync_fileActionMetadata);
  + TableRef table = ObjectStore::table_for_object_type(group, c_sync_fileActionMetadata);
  auto& schema = m_file_action_schema;
  auto obj_key = table->find_first_string(schema.idx_original_name, original_name);
  @@ -297,7 +300,7 @@ void SyncMetadataManager::make_file_action_metadata(StringData original_name,
  obj.set(schema.idx_action, static_cast<int64_t>(action));
  obj.set(schema.idx_url, url);
  obj.set(schema.idx_user_identity, local_uuid);
  - realm->commit_transaction();
  + transaction.commit();
  }
  util::Optional<SyncFileActionMetadata> SyncMetadataManager::get_file_action_metadata(StringData original_name) const
  