Use ImageStyleInterface instead of ImageStyle for type-hinting

Problem/Motivation

Because of this issue #2850373: Incompatibility with remote_stream_wrapper module in the ImageAPI Optimize module there is a need to replace the ImageStyle entity class with another which is compatible and implements ImageStyleInterface. However, the Focal Point module type-hints the concrete implementation \Drupal\image\Entity\ImageStyle in \Drupal\focal_point\Controller\FocalPointPreviewController::buildUrl

class FocalPointPreviewController extends ControllerBase {
...
  /**
   * Create the URL for a preview image including a query parameter.
   *
   * @param \Drupal\image\Entity\ImageStyle $style
     ...
   */
  protected function buildUrl(ImageStyle $style, File $image, $focal_point_value) {
    ...
  }
...
}

This causes the following TypeError

TypeError: Argument 1 passed to Drupal\focal_point\Controller\FocalPointPreviewController::buildUrl() must be an instance of Drupal\image\Entity\ImageStyle, instance of Drupal\entity_decorator\Entity\Replacements\ImageStyle given, called in /var/www/html/docroot/modules/contrib/focal_point/src/Controller/FocalPointPreviewController.php on line 108 in Drupal\focal_point\Controller\FocalPointPreviewController->buildUrl() (line 248 of /var/www/html/docroot/modules/contrib/focal_point/src/Controller/FocalPointPreviewController.php)

Proposed resolution

Change the type-hint to the interface \Drupal\image\ImageStyleInterface

Remaining tasks

Review needed.