feat: add device message about legacy mvbox_move

src/stock_str.rs

@@ -412,6 +412,11 @@ https://delta.chat/donate"))]
 
     #[strum(props(fallback = "Messages in this chat use classic email and are not encrypted."))]
     ChatUnencryptedExplanation = 230,
+
+    #[strum(props(
+        fallback = "You are using the legacy option \"Settings → Advanced → Move automatically to DeltaChat Folder\".\n\nThis option will be removed in a few weeks and you should disable it already today.\n\nIf having chat messages mixed into your inbox is a problem, see https://delta.chat/legacy-move"
+    ))]
+    MvboxMoveDeprecation = 231,
 }
 
 impl StockMessage {
@@ -1223,6 +1228,11 @@ pub(crate) async fn chat_unencrypted_explanation(context: &Context) -> String {
     translated(context, StockMessage::ChatUnencryptedExplanation).await
 }
 
+/// Stock string: `You are using the legacy option "Move automatically to DeltaChat Folder`…
+pub(crate) async fn mvbox_move_deprecation(context: &Context) -> String {
+    translated(context, StockMessage::MvboxMoveDeprecation).await
+}
+
 impl Viewtype {
     /// returns Localized name for message viewtype
     pub async fn to_locale_string(&self, context: &Context) -> String {