Replace drupal_container() with Drupal::service() in the simpletest module

drupal_container() is deprecated, and all calls in the simpletest module need to be replaced with Drupal::service(), except for where the module_handler service is requested, which needs to be replaced with Drupal::moduleHandler() (see #1957154: Replace calls to drupal_container()->get('module_handler') service with Drupal::moduleHandler())

This task a part of #2001206: [META] Replace drupal_container() with Drupal::service() in core modules