Issue #1847002 by tim.plunkett, effulgentsia, msonnabaum: Move entity type classes from Drupal$provider\Plugin\Core\Entity to Drupal$provider\Entity.

Issue #1763974 by tim.plunkett, EclipseGC, berdir, xjm, neclimdul, FabianX: Convert entity type info into plugins.

Dang it. I effed up commit credit. Reverting to I can re-commit again.
Post-push git commit --amend support on d.o would be so lovely.

This reverts commit 722432c3.