feat: Verified 1:1 chats (#4315)

Implement #4188

BREAKING CHANGE: Remove unused DC_STR_PROTECTION_(EN)ABLED* strings
BREAKING CHANGE: Remove unused dc_set_chat_protection()

src/securejoin/bob.rs

@@ -222,6 +222,14 @@ impl BobState {
         let msg = stock_str::contact_verified(context, &contact).await;
         let chat_id = self.joining_chat_id(context).await?;
         chat::add_info_msg(context, chat_id, &msg, time()).await?;
+        chat_id
+            .set_protection(
+                context,
+                ProtectionStatus::Protected,
+                time(),
+                Some(contact.id),
+            )
+            .await?;
         context.emit_event(EventType::ChatModified(chat_id));
         Ok(())
     }