EntityPublishedTrait should use getEntityKey for better performance

Problem/Motivation

In #2498919: Node::isPublished() and Node::getOwnerId() are expensive, it was identified that Node::isPublished is slow, so a cache was introduced through getEntityKey. The issue introduced the following change to isPublished:

+++ b/core/modules/node/src/Entity/Node.php
@@ -258,7 +267,7 @@ public function setSticky($sticky) {
-    return (bool) $this->get('status')->value;
+    return (bool) $this->getEntityKey('status');

and our current implementation is:

  public function isPublished() {
    $key = $this->getEntityType()->getKey('published');
    return (bool) $this->get($key)->value;
  }

Proposed resolution

Make use of getEntityKey in EntityPublishedTrait

Remaining tasks

User interface changes

API changes

Data model changes