Generate keep.xml to prevent resource shrinking on Android (#50620)

Summary:
On Android, when resource shrinking is enabled, all resources added by Metro may be removed as react-native is accessing resources based on strings rather than references, so AGP can't see its usage.

Example output of `android/app/build/outputs/mapping/release/resources.txt `when `shrinkResources` is enabled.
```
raw/__node_modules_expo_vectoricons_build_vendor_reactnativevectoricons_fonts_materialcommunityicons : reachable=false
drawable/__common_assets_haptics_icon : reachable=false
```

It’s a coincidence that most of the resources are currently working, as many file names begin with strings that already exist in the String Pool. For example, `node_modules...` is flagged as used because 'node' is present in the String Pool, causing it to be whitelisted. However, this does not guarantee that the same will apply to all files - especially in a monorepo setup, where paths are significantly different. For example
* `__node_modules_expo_vectoricons_build_vendor_reactnativevectoricons_fonts_materialcommunityicons`
* `__common_assets_haptics_icon`

To prevent that behavior, metro during assets export should create `keep.xml` listing all resources generated by metro.
https://developer.android.com/build/shrink-code#keep-resources

We have already made a similar change in expo cli: https://github.com/expo/expo/pull/35465

## Changelog:

[ANDROID][ADDED] - Generate keep.xml to prevent resource shrinking

Pull Request resolved: https://github.com/facebook/react-native/pull/50620

Test Plan:
1. Enable resource shrinking in RNTester by adding this to `android.buildTypes.release` to `packages/rn-tester/android/app/build.gradle.kts`
```gradle
isMinifyEnabled = true
isShrinkResources = true
```
2. Use some resources in playground, for example:
```diff
 diff --git a/packages/rn-tester/js/examples/Playground/RNTesterPlayground.js b/packages/rn-tester/js/examples/Playground/RNTesterPlayground.js
index 9dbacb99701..9ac9c231f3f 100644
 --- a/packages/rn-tester/js/examples/Playground/RNTesterPlayground.js
+++ b/packages/rn-tester/js/examples/Playground/RNTesterPlayground.js
@@ -11,16 +11,14 @@

 import type {RNTesterModuleExample} from '../../types/RNTesterTypes';

-import RNTesterText from '../../components/RNTesterText';
 import * as React from 'react';
 import {StyleSheet, View} from 'react-native';
+import {Header} from "react-native/Libraries/NewAppScreen";

 function Playground() {
   return (
     <View style={styles.container}>
-      <RNTesterText>
-        Edit "RNTesterPlayground.js" to change this file
-      </RNTesterText>
+      <Header />
     </View>
   );
 }
```

3. Build app using `hermesRelease` variant
4. See Playground screen

| Before | After |
|---|---|
| <img width="488" alt="Zrzut ekranu 2025-04-10 o 12 17 53" src="https://github.com/user-attachments/assets/24fcaa7b-6ddb-4ba6-9fe5-65c27bcbc931" /> | <img width="488" alt="Zrzut ekranu 2025-04-10 o 12 15 58" src="https://github.com/user-attachments/assets/09a1ce77-be26-4571-a4b8-c466bf19e026" /> |

5. Inspect `packages/rn-tester/android/app/build/outputs/mapping/hermesRelease/resources.txt`

| Before | After |
|---|---|
| `drawable/_reactnative_libraries_newappscreen_components_logo : reachable=false` | `drawable/_reactnative_libraries_newappscreen_components_logo : reachable=true` |

Reviewed By: cortinico

Differential Revision: D72960028

Pulled By: huntie

fbshipit-source-id: df725fa2ea50150cd67687a97986976ffbbb5b40

packages/community-cli-plugin/src/commands/bundle/createKeepFileAsync.js

@@ -0,0 +1,40 @@
+/**
+ * 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 type {AssetData} from 'metro/src/Assets';
+
+import assetPathUtils from './assetPathUtils';
+import fs from 'fs';
+import path from 'path';
+
+async function createKeepFileAsync(
+  assets: $ReadOnlyArray<AssetData>,
+  outputDirectory: string,
+): Promise<void> {
+  if (!assets.length) {
+    return;
+  }
+  const assetsList = [];
+  for (const asset of assets) {
+    const prefix = assetPathUtils.drawableFileTypes.has(asset.type)
+      ? 'drawable'
+      : 'raw';
+    assetsList.push(
+      `@${prefix}/${assetPathUtils.getResourceIdentifier(asset)}`,
+    );
+  }
+  const keepPath = path.join(outputDirectory, 'raw/keep.xml');
+  const content = `<resources xmlns:tools="http://schemas.android.com/tools" tools:keep="${assetsList.join(',')}" />\n`;
+  await fs.promises.mkdir(path.dirname(keepPath), {recursive: true});
+  await fs.promises.writeFile(keepPath, content);
+}
+
+export default createKeepFileAsync;