Determine which bundle class should take effect when multiple classes extend the same bundle

Sample exception:

BCA found Drupal\Module1\Entity\Document and Drupal\Module2\Entity\Media\Document
vying to be the bundle class media:document, but one does not extend the other, so a winner
could not be determined. Use the `priority` property on Drupal\bca\Attribute\Bundle with a
value larger than 0 to select which bundle should take priority.

I think I'd like to get ✨ Make $entityType optional: infer from class heirarchy Needs review in first. That refactors the hook implementation out of bca.module and in to its own class. It also has simple logic for setting the plugin ID to the class name, so perhaps we wouldn't need BcaDiscovery?

I think the priority stuff makes sense, I guess without BCA you'd have to put the logic in your own hook_entity_bundle_info_alter and probably also hook_module_implements_alter.

Adding ✨ Use class names instead of plugin IDs Active as related, let's shoot for the moon.

No problem about timing, I just need it for selfish reasons right now. Plan to revisit with whatever goodness we get elsewhere + tests.