Comment::bundleFieldDefintions should throw an Exception if the comment type cannot be loaded

Problem/Motivation

\Drupal\comment\Entity\Comment::bundleFieldDefinitions should throw a fatal error if the comment type cannot be loaded. Continuing in that state puts the site in an unsupported territory and could lead to access issues.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet