Support for Block (display) entities

Hi DamienMcKenna,
Do block entities have a published status boolean field? If so, then we should be able to use (and maybe adapt/update) the Scheduler entity plugin system to provide the functionality. We've done it for Nodes, Media, Commerce Products and Taxonomy Terms. Other 3rd-party entity types have also been made to work with Scheduler.

Before we go too far here, the following issues might help to get done first:
#3282068: Add support for entities without changed date
#3282071: Add support for entities without label_collection key
#3282982: Simplify the scheduler plugin implementations

Do block entities have a published status boolean field?

Block content entitles do have a boolean status field, but they don't expose it as a form element on the entity form. There is work towards this however: https://www.drupal.org/project/drupal/issues/2834546

Just noting for future reference that block entities do not have a bundle, see comments #11-15 on #3282982-11: Simplify the scheduler plugin implementations and #11 on #3225695-11: Support entity types whose entity bundle type does not end with `_type` and entities without created date

Linking to #3355087: Support for non-bundle entities ? but no work has started yet.