Remove usages of EntityManager from EntityViewController

Problem/Motivation

EntityManager is deprecated so let's remove its usages.

Drupal\Core\Entity\Controller\EntityViewController has two subclasses: Drupal\node\Controller\NodePreviewController and Drupal\node\Controller\NodeViewController.

NodeViewController is interesting because it is not used directly, but instead from other controllers, such as Drupal\node\Controller\NodeController, which creates a new instance and then uses its view() method, so it may be a candidate for turning into a trait.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes