Disallow group names longer than 32 extended graphemes

ts/Intl.d.ts

@@ -0,0 +1,27 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+declare namespace Intl {
+  type SegmenterOptions = {
+    granularity?: 'grapheme' | 'word' | 'sentence';
+  };
+
+  type SegmentData = {
+    index: number;
+    input: string;
+    segment: string;
+  };
+
+  interface Segments {
+    containing(index: number): SegmentData;
+
+    [Symbol.iterator](): Iterator<SegmentData>;
+  }
+
+  // `Intl.Segmenter` is not yet in TypeScript's type definitions, so we add it.
+  class Segmenter {
+    constructor(locale?: string, options?: SegmenterOptions);
+
+    segment(str: string): Segments;
+  }
+}