Create new revision by default

The box description request moved under #2900886: Title field label and box type description
The "field_body to new box types automatically" is a too specific request, which does not seems useful any more.

To fully enforce box revisions (hiding the "Create new revision" checkbox) the following hook needs to be implemented. Similarly as for node revisions.

/**
 * Implements hook_entity_field_access()
 */
function MYMODULE_entity_field_access($operation, FieldDefinitionInterface $field_definition, AccountInterface $account, FieldItemListInterface $items = NULL) {
  if ($account->hasPermission('administer box entities') || $account->hasPermission('delete all box revisions')) {
    return AccessResult::neutral();
  }

  if ($operation == 'update' && $items->getName() === 'vid' && $items->getEntity()->getEntityTypeId() === 'box') {
    return AccessResult::forbidden();
  }
  return AccessResult::neutral();
}