Prepare for Jest 27+ by making legacy fake timer use explicit

Summary:
Jest 27 [flips defaults](https://jestjs.io/blog/2021/05/25/jest-27#flipping-defaults), making "modern" fake timers (ie, `sinonjs/fake-timers`) the default, over "legacy", which we currently use.

We're not quite ready for modern timers yet, partly due to Promise polyfills (https://github.com/facebook/react-native/pull/34659), and also some internal issues with specific tests.

This makes our use of legacy timers explicit in preparation for an update to Jest. A switch to modern timers may follow later.

Changelog:
[Internal][Changed] - Prepare for Jest 27+ by making legacy fake timer use explicit

Reviewed By: jacdebug

Differential Revision: D39383719

fbshipit-source-id: 6a3dc6f8547cc76f7702a5a39c9b30a184303f17

Libraries/Interaction/__tests__/InteractionManager-test.js

@@ -168,7 +168,7 @@ describe('promise tasks', () => {
   }
   beforeEach(() => {
     jest.resetModules();
-    jest.useFakeTimers();
+    jest.useFakeTimers('legacy');
     InteractionManager = require('../InteractionManager');
     BatchedBridge = require('../../BatchedBridge/BatchedBridge');
     sequenceId = 0;

flow/jest.js

@@ -900,7 +900,7 @@ type JestObjectType = {
    * (setTimeout, setInterval, clearTimeout, clearInterval, nextTick,
    * setImmediate and clearImmediate).
    */
-  useFakeTimers(): JestObjectType,
+  useFakeTimers(type?: 'legacy' | 'modern'): JestObjectType,
   /**
    * Instructs Jest to use the real versions of the standard timer functions.
    */

jest.config.js

@@ -16,7 +16,7 @@ module.exports = {
     '.*': './jest/private/preprocessor.js',
   },
   setupFiles: ['./jest/setup.js'],
-  timers: 'fake',
+  timers: 'legacy',
   testRegex: '/__tests__/.*-test\\.js$',
   testPathIgnorePatterns: [
     '/node_modules/',