Don't create always rejecting promises for timeout

Summary:
Our existing `timeout` implementation was always throwing an exception, due to sleeping and then throw an exception, which is than handled but ignored by `Promise.race`.

This implementation has a few problems

1. Because it always throws, having a debugger session with 'break on caught exceptions' will pause on every usage of timeout (rather than just the ones that actually timeout). This makes this way of debugging a bit useless.
2. Throwing exceptions is in principle an expensive process (due to the stack trace generation)
3. Not cancelling the timeout used by sleep is a bit of a waste as well

Reviewed By: lawrencelomax

Differential Revision: D33982717

fbshipit-source-id: d739c02112e1c1bc4cd691af852371d08a99abc6

desktop/flipper-common/src/__tests__/timeout.node.tsx

@@ -0,0 +1,34 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {timeout} from '../utils/timeout';
+
+test('resolves', async () => {
+  const p = Promise.resolve(3);
+
+  await expect(timeout(100, p)).resolves.toBe(3);
+});
+
+test('rejects', async () => {
+  const p = Promise.reject(new Error('oops'));
+
+  await expect(timeout(100, p)).rejects.toMatchInlineSnapshot(`[Error: oops]`);
+});
+
+test('times out', async () => {
+  let lateResolve: any;
+  const p = new Promise((r) => {
+    lateResolve = r;
+  });
+
+  await expect(timeout(100, p)).rejects.toMatchInlineSnapshot(
+    `[Error: Timed out in 100 ms.]`,
+  );
+  lateResolve(); // avoid dangling promise after test
+});