[12.x] Introduce Job@resolveQueuedJobClass()

[cosmastech]

This will resolve: #54502

This adds a method to the Job interface which is used for determining the class-name for the wrapped job. Job@resolveName() was modified to return the displayName, which works for most cases. However, when we are checking if a Job should be silently deleted if a model no longer exists, we use reflection. Since the displayName may not be a class, this won't work.

Alternate solution

To avoid modifying the contract on the Job interface, we could simply add another check to CallQueuedHandler@handleModelNotFound() where it checks that the class exists before we reflect the $class name.