[Hocuri]

Part of #8775

TODO:

• Make it impossible already to send and receive unencrypted
• Check which parts of refactor: New fingerprints can't be empty anymore #8809 I need already in this first PR
• A website with more info that's linked at the end of the device message ("Read more: https://...")

Things I considered but didn't implement:

• Rather than removing all members from ad-hoc groups, we could remove only ContactID::SELF. This would be enough for making them read-only, but it doesn't really matter. The sender of a message can be seen by tapping on the sender avatar of a message.
• Inline create_and_deduplicate_from_bytes() so that the migration doesn't depend on external code. Seems fine as-is; if we ever remove create_and_deduplicate_from_bytes(), we can just remove the respective code from the migration.

Future possibilities (please comment if we should do some of them already):

• Give all of the ad-hoc groups a fake group ID, so that we don't need any special code for handling empty group IDs

  • If so, need to test what happens when the group ID is not the same on different devices, and then the user pins the chat on one of the devices
    • E.g. we might use the newest msgid as an identifier, which will often/sometimes be the same on different devices:

      UPDATE chats
      SET grpid='legacy_group_' || coalesce(
          (SELECT NULLIF(rfc724_mid, '') FROM msgs WHERE chat_id=chats.id ORDER BY id DESC LIMIT 1),
          hex(randomblob(16))
      )
      WHERE id IN (SELECT chat_id FROM legacy_unencrypted_chats) AND grpid='';
      

• Similarly, give all of the address-contacts a fake fingerprint