feat: Make broadcast lists create their own chat (#4644)

feat: Make broadcast lists create their own chat - UIs need to ask for
the name when creating broadcast lists now (see
https://github.com/deltachat/deltachat-android/pull/2653)

That's quite a minimal approach: Add a List-ID header to outgoing
broadcast lists, so that the receiving Delta Chat shows them as a
separate chat, as talked about with @r10s and @hpk42.

Done:
- [x] Fix an existing bug that the chat name isn't updated when the
broadcast/mailing list name changes (I already started this locally)

To be done in other PRs:
- [ ] Right now the receiving side shows "Mailing list" in the subtitle
of such a chat, it would be nicer if it showed "Broadcast list" (or
alternatively, rename "Broadcast list" to "Mailing list", too)
- [ ] The UIs should probably ask for a name before creating the
broadcast list, since it will actually be sent over the wire. (Android
PR: https://github.com/deltachat/deltachat-android/pull/2653)

Fixes https://github.com/deltachat/deltachat-core-rust/issues/4597

BREAKING CHANGE: This means that UIs need to ask for the name when creating a broadcast list, similar to https://github.com/deltachat/deltachat-android/pull/2653.

src/chat.rs

@@ -6094,22 +6094,40 @@ mod tests {
             get_chat_contacts(&alice, chat_bob.id).await?.pop().unwrap(),
         )
         .await?;
-        let chat = Chat::load_from_db(&alice, broadcast_id).await?;
-        assert_eq!(chat.typ, Chattype::Broadcast);
-        assert_eq!(chat.name, stock_str::broadcast_list(&alice).await);
-        assert!(!chat.is_self_talk());
+        set_chat_name(&alice, broadcast_id, "Broadcast list").await?;
+        {
+            let chat = Chat::load_from_db(&alice, broadcast_id).await?;
+            assert_eq!(chat.typ, Chattype::Broadcast);
+            assert_eq!(chat.name, "Broadcast list");
+            assert!(!chat.is_self_talk());
 
-        send_text_msg(&alice, broadcast_id, "ola!".to_string()).await?;
-        let msg = alice.get_last_msg().await;
-        assert_eq!(msg.chat_id, chat.id);
+            send_text_msg(&alice, broadcast_id, "ola!".to_string()).await?;
+            let msg = alice.get_last_msg().await;
+            assert_eq!(msg.chat_id, chat.id);
+        }
 
-        let msg = bob.recv_msg(&alice.pop_sent_msg().await).await;
-        assert_eq!(msg.get_text(), "ola!");
-        assert!(!msg.get_showpadlock()); // avoid leaking recipients in encryption data
-        let chat = Chat::load_from_db(&bob, msg.chat_id).await?;
-        assert_eq!(chat.typ, Chattype::Single);
-        assert_eq!(chat.id, chat_bob.id);
-        assert!(!chat.is_self_talk());
+        {
+            let msg = bob.recv_msg(&alice.pop_sent_msg().await).await;
+            assert_eq!(msg.get_text(), "ola!");
+            assert_eq!(msg.subject, "Broadcast list");
+            assert!(!msg.get_showpadlock()); // avoid leaking recipients in encryption data
+            let chat = Chat::load_from_db(&bob, msg.chat_id).await?;
+            assert_eq!(chat.typ, Chattype::Mailinglist);
+            assert_ne!(chat.id, chat_bob.id);
+            assert_eq!(chat.name, "Broadcast list");
+            assert!(!chat.is_self_talk());
+        }
+
+        {
+            // Alice changes the name:
+            set_chat_name(&alice, broadcast_id, "My great broadcast").await?;
+            let sent = alice.send_text(broadcast_id, "I changed the title!").await;
+
+            let msg = bob.recv_msg(&sent).await;
+            assert_eq!(msg.subject, "Re: My great broadcast");
+            let bob_chat = Chat::load_from_db(&bob, msg.chat_id).await?;
+            assert_eq!(bob_chat.name, "My great broadcast");
+        }
 
         Ok(())
     }