Migrating RNTester to Packages Directory (#29567)

Summary:
## Changelog

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This PR aims to migrate the RNTester App to `packages` directory. But is currently, open to inspect the CI issues and resolve the merge conflicts.

Currently done
 - Working on iOS
 - Working on Android
 - Detox Tests working on iOS

Need to work on
 - Errors generated by the CI builds

[General] [Changed] - Migrated the RNTester App to the packages directory.

Pull Request resolved: https://github.com/facebook/react-native/pull/29567

Test Plan: It runs on both ios and android for now and the detox iOS builds are working.

Reviewed By: cpojer

Differential Revision: D23034761

Pulled By: rickhanlonii

fbshipit-source-id: e04bb06e1c7ef15d340206090d1575a871b9e6f5

packages/rn-tester/NativeModuleExample/NativeScreenshotManager.js

@@ -0,0 +1,28 @@
+/**
+ * Copyright (c) Facebook, Inc. and its 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
+ */
+
+'use strict';
+
+import type {TurboModule} from '../../../Libraries/TurboModule/RCTExport';
+import * as TurboModuleRegistry from '../../../Libraries/TurboModule/TurboModuleRegistry';
+
+export interface Spec extends TurboModule {
+  +getConstants: () => {||};
+  takeSnapshot(id: string): Promise<string>;
+}
+
+const NativeModule = TurboModuleRegistry.get<Spec>('ScreenshotManager');
+
+export function takeSnapshot(id: string): Promise<string> {
+  if (NativeModule != null) {
+    return NativeModule.takeSnapshot(id);
+  }
+  return Promise.reject();
+}