Issue #3412951 by DYdave: Automated testing on GitLab CI: Fixed PHPStan errors...

https://www.drupal.org/project/image_link_formatter/issues/3412951

Automated testing on GitLab CI:

• Fixed PHPStan errors Unsafe usage of new static(). by declaring plugin constructor methods as final.
• Updated module's documentation to explain how its FieldFormatter plugin classes could be extended.

responsive_image_link_formatter/src/Plugin/Field/FieldFormatter/ResponsiveImageLinkFormatter.php

@@ -71,7 +71,7 @@ class ResponsiveImageLinkFormatter extends ResponsiveImageFormatter implements C
    * @param \Drupal\Core\Entity\EntityFieldManagerInterface $entity_field_manager
    *   The entity field manager service.
    */
-  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, EntityStorageInterface $responsive_image_style_storage, EntityStorageInterface $image_style_storage, LinkGeneratorInterface $link_generator, AccountInterface $current_user, EntityFieldManagerInterface $entity_field_manager) {
+  final public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, EntityStorageInterface $responsive_image_style_storage, EntityStorageInterface $image_style_storage, LinkGeneratorInterface $link_generator, AccountInterface $current_user, EntityFieldManagerInterface $entity_field_manager) {
     parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings, $responsive_image_style_storage, $image_style_storage, $link_generator, $current_user);
     $this->entityFieldManager = $entity_field_manager;
   }