Handle Surrogate Pairs in truncate() (#25148)

app/javascript/mastodon/features/status/index.jsx

@@ -166,8 +166,9 @@ const makeMapStateToProps = () => {
 };
 
 const truncate = (str, num) => {
-  if (str.length > num) {
-    return str.slice(0, num) + '…';
+  const arr = Array.from(str);
+  if (arr.length > num) {
+    return arr.slice(0, num).join('') + '…';
   } else {
     return str;
   }