|Issue tags:||API clean-up|
#1763974: Convert entity type info into plugins and #1828852: Update entity class names after the conversion to plugins saw a lot of push back on converting entity types into plugins, with good reason.
All we want from the plugin system so far is the discoverability.
This is a first attempt toward doing that, but entity specific.
Because plugins need to be in a separate directory from other non-plugins, I've changed the namespace from Plugin\Core\Entity to EntityType.
So, Node.php now lives at core/modules/node/lib/Drupal/node/EntityType/Node.php, and it is
use Drupal\node\EntityType\Node; for using it.
A majority of this is renaming those namespaces, git diff --color-words will help here.