"Draft available" text still appears after deleting a forward revision

Problem/Motivation

The Draft available state label displays after deleting a forward revision.

Steps to reproduce:

1. Create and publish a page
2. Create a forward revision (draft)
3. Draft available label shows for moderation sidebar text
4. Delete the draft through the revisions page
5. Draft available label still displays

This is a caching issue, I don't think there are any contexts or tags we can use for revisions so this will require manual purging.

Proposed resolution

Possibly implement hook_ENTITY_TYPE_revision_delete and purge the entity's cache tags.

Another possible solution would be to add our own cache tag and purge that instead (may be more performant).

Remaining tasks

1. Agree on approach
2. Add tests
3. Add fix