Add optional BatchOperations method calls to perform pre and post batch

The ability to add the following methods to your custom Batch Operation class has been added.

/**
   * Optional method that is called once BEFORE the run of the batch.
   *
   * This can be used to turn on maintenance mode, disable indexing, or
   * anything else that needs to be done before running the BatchOperation.
   *
   * @param array $sandbox
   *   The sandbox by reference. Used for keeping state in the batch.
   *
   * @return string
   *   A message that will be added to the BatchOpLog
   */
  public function preBatchMethod(&$sandbox): string;

  /**
   * Optional method that is called once AFTER the run of the batch.
   *
   * This can be used to undo anything that was done in preBatchMethod(). Like
   * turn off maintenance mode, re-enable indexing, or
   * anything else that needs to be done after running the BatchOperation.
   *
   * @param array $sandbox
   *   The sandbox by reference. Used for keeping state in the batch.
   *
   * @return string
   *   A message that will be added to the BatchOpLog
   */
  public function postBatchMethod(&$sandbox): string;

This has been released with 1.0.1-beta8 →