feat: When reactions are seen, remove notification from second device (#6480)

Instead of being trashed, the message containing a reaction remains in the chat, hidden and InFresh. When the chat is opened, it will be marked as Seen on the server, so that a second device removes the notifications for the reaction.

Close https://github.com/deltachat/deltachat-core-rust/issues/6210.

Also, this adds a benchmark.

src/test_utils.rs

@@ -607,6 +607,19 @@ impl TestContext {
         msg
     }
 
+    /// Receive a message using the `receive_imf()` pipeline. Panics if it's not hidden.
+    pub async fn recv_msg_hidden(&self, msg: &SentMessage<'_>) -> Message {
+        let received = self
+            .recv_msg_opt(msg)
+            .await
+            .expect("receive_imf() seems not to have added a new message to the db");
+        let msg = Message::load_from_db(self, *received.msg_ids.last().unwrap())
+            .await
+            .unwrap();
+        assert!(msg.hidden);
+        msg
+    }
+
     /// Receive a message using the `receive_imf()` pipeline. This is similar
     /// to `recv_msg()`, but doesn't assume that the message is shown in the chat.
     pub async fn recv_msg_opt(