In Drupal 7 I could go to any entity's "manage display" and choose "expert" or "minimal," etc. 

In Drupal 8, I can see a Twig template for expert, and a Plugin for expert (ex.g.) as well. But how do I get the UI where I can choose 'expert'?

If it's no longer in the UI, how do I implement my own Plugin? How can I write twig for just that field? If I'm doing that, why do I need Display Suite anyway (as I'm just using a one-col layout)? Do I?