Issue #3605986 by dydave: Added support for Drupal 12.

https://www.drupal.org/project/image_link_formatter/issues/3605986

Support for Drupal 12:

• Core version requirements: Added support for 12.
• Normalized file composer.json.
• Added declare(strict_types=1); in all PHP files and types where needed.
• Added attributes Group and RunTestsInSeparateProcesses to all tests files.
• Added Gitlab CI phpstan (previous major) job before script commands to remove attributes Group and RunTestsInSeparateProcesses to prevent raising errors for D10.
• Removed __constructor methods to inject dependencies in the create methods instead.
• Added several rounds of improvements suggested by AI:
  • Removed redundant implementation of ContainerFactoryPluginInterface.
  • Added missing variable types.
  • Added cached result of getLinkFieldsOptions(), populated on first call.
  • Improved string escaping in method settingsSummary.
  • Changed method's getLinkFieldsOptions identified from private to protected which is more appropriate for Trait.
  • Replaced use of \Drupal::service with $this->container->get wherever possible.