[PP-2] Add revision support

As pointed out in https://www.mediacurrent.com/blog/editorial-workflow-head-head-paragraph..., one of the lacking features for Entity Embed is ensuring that we're embedding a specific revision, if desired. At the first step, we should add support for a new data-entity-revision property and if it's available, use it to load the correct revision.

I'm not sure how the UI should work for this, but I'm going to look into https://www.drupal.org/project/entity_reference_revisions → and see how that project handles it. Might also make another good use case for #2705893: [entity_browser] Allow the dialog form to be swapped via plugin to support alternate workflows (decouple Entity Browser handling from EntityEmbedDialog) → if a revision-based selection ends up being more advanced.