Add forward-compatibility for deprecation of check_markup

Problem/Motivation

Drupal 11.4 deprecates check_markup(), and it will be removed in Drupal 12, per https://www.drupal.org/node/3588040 . This module uses check_markup() in a Trait in its testing suite. For convenience, Drupal provides the \Drupal\Tests\filter\Traits\ProcessedTextTestTrait trait with a helper method, facilitating testing.

We should update the test logic to make use of the new helper method, while supporting versions of Drupal core prior to 11.4 by using the deprecated check_markup() method. Although Drupal core provided a new DeprecationHelper method to facilitate this kind of thing, that was introduced in Drupal 10.1, and since this module's 2.0.x branch currently declares compatibility with Drupal 9, we should use the "old" way of checking Drupal versions (e.g., if (version_compare(\Drupal::VERSION, '9.4', '>=')) {).

Proposed resolution

Add the ProcessedTextTestTrait to the Pathologic Test Trait and add version compare logic to use either check_markup or $this->processText

Remaining tasks

N/A

User interface changes

N/A

API changes

N/A

Data model changes

N/A