Add RevisionableStorageInterface::createRevision generic for return type (#894)

* createRevision returns an object instance of the same type passed to entity, but not the same object reference

I cannot add stubs for RevisionableStorageInterface and TranslatableRevisionableStorageInterface in my own projects because phpstan-drupal prevents it!

* `TranslatableRevisionableStorageInterface::createRevision` has a different signature and may require it

* typing

* another type

Author: dpi

stubs/Drupal/Core/Entity/RevisionableStorageInterface.stub

@@ -14,5 +14,12 @@ interface RevisionableStorageInterface extends EntityStorageInterface {
    * @param int|numeric-string $revision_id
    */
   public function deleteRevision($revision_id): void;
+  
+  /**
+   * @param R $entity
+   * @return R
+   * @template R of \Drupal\Core\Entity\RevisionableInterface
+   */
+  public function createRevision(RevisionableInterface $entity, bool $default = TRUE);
 
 }

stubs/Drupal/Core/Entity/TranslatableRevisionableStorageInterface.stub

@@ -9,4 +9,11 @@ namespace Drupal\Core\Entity;
 // This is fragile and relies on `ContentEntityStorageInterface` only implementing this interface.
 interface TranslatableRevisionableStorageInterface extends RevisionableStorageInterface, TranslatableStorageInterface {
 
+  /**
+   * @param R $entity
+   * @return R
+   * @template R of \Drupal\Core\Entity\RevisionableInterface
+   */
+  public function createRevision(RevisionableInterface $entity, bool $default = TRUE, ?bool $keep_untranslatable_fields = NULL);
+  
 }