Disallow group names longer than 32 extended graphemes

ts/util/grapheme.ts

@@ -0,0 +1,13 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+export function count(str: string): number {
+  const segments = new Intl.Segmenter().segment(str);
+  const iterator = segments[Symbol.iterator]();
+
+  let result = -1;
+  for (let done = false; !done; result += 1) {
+    done = Boolean(iterator.next().done);
+  }
+  return result;
+}