Rename ReactNativeTester as just Fantom (#48142)

Summary:
Pull Request resolved: #48142

Changelog: [internal]

This is the default export from the `react-native/fantom` package and it makes sense to be called that way. Also, this is similar to the `jest` global.

Reviewed By: javache

Differential Revision: D66874225

fbshipit-source-id: 8b43a637ebb42b5b1acb9ea5a6dbedd4c1a4f9e0

Author: rubennorte

jest/integration/runtime/WarmUpEntryPoint.js

@@ -4,6 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
+ * @flow strict-local
  * @format
  * @oncall react_native
  */
@@ -13,5 +14,5 @@
  */
 
 import 'react-native/Libraries/Core/InitializeCore.js';
-import 'react-native/src/private/__tests__/ReactNativeTester';
+import '@react-native/fantom/src/__tests__/Fantom-itest';
 import './setup';

packages/react-native-fantom/src/__tests__/ReactNativeTester-itest.js renamed to packages/react-native-fantom/src/__tests__/Fantom-itest.js

@@ -14,7 +14,7 @@ import {createRoot, runTask} from '..';
 import * as React from 'react';
 import {Text, View} from 'react-native';
 
-describe('ReactNativeTester', () => {
+describe('Fantom', () => {
   describe('runTask', () => {
     it('should run a task synchronously', () => {
       const task = jest.fn();