Convert signal.js and preload.js to Typescript

ts/windows/main/preload_test.ts

@@ -0,0 +1,28 @@
+// Copyright 2021-2022 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+/* eslint-disable no-console */
+
+import { ipcRenderer as ipc } from 'electron';
+import { sync } from 'fast-glob';
+
+// eslint-disable-next-line import/no-extraneous-dependencies
+import { assert } from 'chai';
+
+window.assert = assert;
+
+// This is a hack to let us run TypeScript tests in the renderer process. See the
+//   code in `test/index.html`.
+
+window.testUtilities = {
+  onComplete(info) {
+    return ipc.invoke('ci:test-electron:done', info);
+  },
+  prepareTests() {
+    console.log('Preparing tests...');
+    sync('../../test-{both,electron}/**/*_test.js', {
+      absolute: true,
+      cwd: __dirname,
+    }).forEach(require);
+  },
+};