Add Playground test (#51220)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/51220

Changelog: [internal]

Just a playground file to do quick tests in the Fantom environment.

For example, I just used it to know if Hermes supports `AggregateError`, which does:

```
  it('...', () => {
    console.log('AggregateError', global.AggregateError);
  });
```

{F1977824992}

Reviewed By: lenaic

Differential Revision: D74474870

fbshipit-source-id: cbe8a287738b09afe336ae479cc3105d1474e58b

packages/react-native-fantom/src/__tests__/Playground-itest.js

@@ -0,0 +1,21 @@
+/**
+ * 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.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';
+
+// eslint-disable-next-line no-unused-vars
+import * as Fantom from '@react-native/fantom';
+
+describe('Playground', () => {
+  it('...', () => {
+    // Add your tests here, but do NOT commit them.
+  });
+});