Replace CKEditor Model with ViewModel for Drupal 10.3 compatibility

The merge request has a fix, though this may cause problems with backward compatibility. This is a similar issue to 🐛 CKEditor 5 41.3.1 (Drupal 10.3 beta) breaking change Fixed ; we may need to do something like the fix in this issue to resolve the backward compatibility problem.

Mine says "TypeError: t.Model is not a constructor". I think the patch resolved it.

I created a new release branch 1.2.x to avoid breaking existing installations.

Automatically closed - issue fixed for 2 weeks with no activity.