checks for bundle entity classes should happen in rebuild, not runtime

Doesn't seem like a novice level issue so removing that tag.

Fixed the two comments on the MR.

However, there is another problem:

          if ($bundle_entity_type = $entity_type->getBundleEntityType()) {
            foreach ($this->entityTypeManager->getStorage($bundle_entity_type)->loadMultiple() as $entity) {

Bundles are not necessarily entities! Modules can use hook_entity_bundle_info() to define bundles for an entity type, without using a config entity to define them.

The code is currently only handling the bundle entity case, and not handling code-defined bundles at all.

Fix coming.

Updated the tests.

This is ready but MR needs repointing.

Believe the MR needs to be updated to 11.x

Fixed the phpcs issue but appears to have test failures.