feat: add "e2ee encrypted" info message to all e2ee chats (#7008)

this PR adds a info message "messages are end-to-end-encrypted" also for
chats created by eg. vcards. by the removal of lock icons, this is a
good place to hint for that in addition; this is also what eg. whatsapp
and others are doing

the wording itself is tweaked at
https://github.com/deltachat/deltachat-android/pull/3817 (and there is
also the rough idea to make the message a little more outstanding, by
some more dedicated colors)

~~did not test in practise, if this leads to double "e2ee info messages"
on secure join, tests look good, however.~~ EDIT: did lots of practise
tests meanwhile :)

most of the changes in this PR are about test ...

ftr, in another PR, after 2.0 reeases, there could probably quite some
code cleanup wrt set-protection, protection-disabled etc.

---------

Co-authored-by: Hocuri <hocuri@gmx.de>

src/chat.rs

@@ -349,6 +349,8 @@ impl ChatId {
             chat_id
                 .add_protection_msg(context, ProtectionStatus::Protected, None, timestamp)
                 .await?;
+        } else {
+            chat_id.maybe_add_encrypted_msg(context, timestamp).await?;
         }
 
         info!(
@@ -604,6 +606,42 @@ impl ChatId {
         Ok(())
     }
 
+    /// Adds message "Messages are end-to-end encrypted" if appropriate.
+    ///
+    /// This function is rather slow because it does a lot of database queries,
+    /// but this is fine because it is only called on chat creation.
+    async fn maybe_add_encrypted_msg(self, context: &Context, timestamp_sort: i64) -> Result<()> {
+        let chat = Chat::load_from_db(context, self).await?;
+
+        // as secure-join adds its own message on success (after some other messasges),
+        // we do not want to add "Messages are end-to-end encrypted" on chat creation.
+        // we detect secure join by `can_send` (for Bob, scanner side) and by `blocked` (for Alice, inviter side) below.
+        if !chat.is_encrypted(context).await?
+            || self <= DC_CHAT_ID_LAST_SPECIAL
+            || chat.is_device_talk()
+            || chat.is_self_talk()
+            || (!chat.can_send(context).await? && !chat.is_contact_request())
+            || chat.blocked == Blocked::Yes
+        {
+            return Ok(());
+        }
+
+        let text = stock_str::messages_e2e_encrypted(context).await;
+        add_info_msg_with_cmd(
+            context,
+            self,
+            &text,
+            SystemMessage::ChatE2ee,
+            timestamp_sort,
+            None,
+            None,
+            None,
+            None,
+        )
+        .await?;
+        Ok(())
+    }
+
     /// Sets protection and adds a message.
     ///
     /// `timestamp_sort` is used as the timestamp of the added message
@@ -2673,6 +2711,10 @@ impl ChatIdBlocked {
                     smeared_time,
                 )
                 .await?;
+        } else {
+            chat_id
+                .maybe_add_encrypted_msg(context, smeared_time)
+                .await?;
         }
 
         Ok(Self {