Fix phpstan errors

Fixed phpstan issues in MR !8, few errors still needs to be fixed.

  Line   src/EntityHandlers/MicrocontentModerationHandler.php              
 ------ ------------------------------------------------------------------ 
  11     Class                                                             
         Drupal\microcontent\EntityHandlers\MicrocontentModerationHandler  
         extends @internal class                                           
         Drupal\content_moderation\Entity\Handler\ModerationHandler.       
 ------ ------------------------------------------------------------------ 

 ------ ------------------------------------------------------------------------- 
  Line   src/Plugin/BackFillQuery/MicroContentHandler.php                         
 ------ ------------------------------------------------------------------------- 
  15     Class Drupal\microcontent\Plugin\BackFillQuery\MicroContentHandler       
         extends unknown class                                                    
         Drupal\backfill_formatter\Plugin\BackFillQuery\PermissionStatusHandler.  
         💡 Learn more at https://phpstan.org/user-guide/discovering-symbols      
 ------ ------------------------------------------------------------------------- 

Class                                                             
         Drupal\microcontent\EntityHandlers\MicrocontentModerationHandler  
         extends @internal class                                           
         Drupal\content_moderation\Entity\Handler\ModerationHandle

This can be ignored

Class Drupal\microcontent\Plugin\BackFillQuery\MicroContentHandler       
         extends unknown class                                                    
         Drupal\backfill_formatter\Plugin\BackFillQuery\PermissionStatusHandler

Likely need require-dev for backfill_formatter

Looking at the PHPStan and PHPCS report there is still quite some room for improvement.

@sourabhjain This is our second encounter today where you are just applying merge request remarks/code suggestions without really taking into account the bigger picture. This seems to be a recurring thing in your contributions, multiple people 📌 Add validation constraints to block_content.type.* Needs work have been trying to explain this to you already.