Give pending entities BBIDs and treat them the same way as regular entities

[kellnerd]

Problem

Pending entities are identified by a numeric ID instead of a BBID as regular entities.
Besides making it impossible for pending entities to be used in relationships, this requires separate logic to load data (for display or editing) and to store it (after approval).
Having this separate logic which is almost identical but shares almost no code with regular entities is very annoying as every change for an entity type has to be done in two places.

Solution

1. Schema change to give pending imports a BBID already
   • Merge the import entry table into the entity table (since they both have the same columns now)
   • Add a boolean column to distinguish pending imports and accepted entities and use it for all entity views
   • Give import tables and columns more descriptive names (2c5b3ef)
   • Also integrate import views into the entity views which are used to load and update entities (66aae22)
2. Adapt ORM (Adapt to pending entities with BBIDs / Introducing Kysely bookbrainz-data-js#323) and website to these changes
3. Display imports via the regular entity pages
   • Thanks to the combined entity views this requires only a bit of fine-tuning! (e107640)
   • Hide irrelevant buttons and actions which don't make sense for pending imports
   • Show the proper footer to approve or discard the import instead of the regular entity actions
   • Move and adapt the approve/discard routes to the regular entity routers
4. Completely rewrite the approval function to preserve the BBID which was already assigned (see Adapt to pending entities with BBIDs / Introducing Kysely bookbrainz-data-js#323 and 3541746)

Now that imported entities have BBIDs instead of numeric IDs, they can finally have relationships (either with other pending imports or with already accepted entities).

Since we are using the combined entity views, we can also load imports into the entity editor without any changes! In order to make editing of pending entities (Edit & Approve) work, we only have to do minimal changes in the edit handler:

• Approve the import for an initial revision before creating a new "Edit" revision as usual (b2c0577)
• Exit early if the entity is approved without additional changes and avoid creating an empty revision (9dd8b51)

Finally I had the enormous pleasure to delete a ton of unused code (d9830e5).

Areas of Impact

Literally everything since I have tampered with the core schema and entity loading.

P.S. You might have to temporarily yarn add kysely in bb-site because apparently yarn link does not take changed dependencies in your linked local bb-data version into account.