compute_publish_state -> has_published_version

LMS-11213

@nasthagiri @cpennington one or both please review
Can further simplify?
```
  if getattr(xblock, 'is_draft', False):
             try:
                 xblock.runtime.lookup_item(as_published(xblock.location))
             except ItemNotFoundError:
                return False
  return True
```