Drupal 11 compatibility and address phpstan issues from pipeline

Problem/Motivation

A number phpstan warnings appear in the pipeline with the addition of gitlab ci in #3516929: Add GitLab CI.

Address the following:

------ ----------------------------------------------------------------------- 
  Line   src/Entity/MediaLinkEnhancementsMedia.php                              
 ------ ----------------------------------------------------------------------- 
  21     Instantiated class                                                     
         Drupal\media_link_enhancements\Entity\EntityMalformedException not     
         found.                                                                 
         🪪  class.notFound                                                     
         💡  Learn more at https://phpstan.org/user-guide/discovering-symbols   
  29     Call to method isDefaultRevision() on an unknown class                 
         Drupal\media_link_enhancements\Entity\RevisionableInterface.           
         🪪  class.notFound                                                     
         💡  Learn more at https://phpstan.org/user-guide/discovering-symbols   
  29     Class Drupal\media_link_enhancements\Entity\RevisionableInterface not  
         found.                                                                 
         🪪  class.notFound                                                     
         💡  Learn more at https://phpstan.org/user-guide/discovering-symbols   
  63     Instantiated class                                                     
         Drupal\media_link_enhancements\Entity\UndefinedLinkTemplateException   
         not found.                                                             
         🪪  class.notFound                                                     
         💡  Learn more at https://phpstan.org/user-guide/discovering-symbols   
 ------ ----------------------------------------------------------------------- 
 ------ ---------------------------------------------------------------------- 
  Line   src/Form/MediaLinkEnhancementsAdminForm.php                           
 ------ ---------------------------------------------------------------------- 
  70     Method Drupal\Core\Form\ConfigFormBase::__construct() invoked with 1  
         parameter, 2 required.                                                
         🪪  arguments.count                                                   
 ------ ---------------------------------------------------------------------- 
 ------ ----------------------------------------------------------------------- 
  Line   src/Plugin/Linkit/Matcher/MediaLinkEnhancementsMediaEntityMatcher.php  
 ------ ----------------------------------------------------------------------- 
  18     Class                                                                  
         Drupal\media_link_enhancements\Plugin\Linkit\Matcher\MediaLinkEnhance  
         mentsMediaEntityMatcher extends unknown class                          
         Drupal\linkit\Plugin\Linkit\Matcher\EntityMatcher.                     
         💡  Learn more at https://phpstan.org/user-guide/discovering-symbols   
  42     \Drupal calls should be avoided in classes, use dependency injection   
         instead                                                                
         🪪  globalDrupalDependencyInjection.useDependencyInjection             
 ------ ----------------------------------------------------------------------- 
 ------ ----------------------------------------------------------------------- 
  Line   src/Routing/MediaLinkEnhancementsUrlGenerator.php                      
 ------ ----------------------------------------------------------------------- 
  187    Call to an undefined method                                            
         Drupal\media_link_enhancements\Routing\MediaLinkEnhancementsUrlGenera  
         tor::getRouteDebugMessage().                                           
         🪪  method.notFound                                                    
 ------ ----------------------------------------------------------------------- 
 [ERROR] Found 8 errors