Batch's database backend is a core service but it depends on system install

In system_schema() we create a batch table. We should change Drupal\Core\Batch\BatchStorage to only create a table if necessary - this means that alternate batch implementations can safely remove the batch table and know that if the site swaps back to the BatchStorage the table will be created.

Also making this change encapsulates the storage to the backend which is good for general sanity.