Post-process build files for React Native to add generated signature and @nolint (#26616)

## Summary

We're enabling a new mechanism to synchronize build files from `react`
to `react-native`. That new mechanism doesn't post-process files, so we
need to add that post-processing somewhere. This PR does that when
generating the files in the first place, so the generated files in the
`build` directory are ready to be committed in the `react-native`
repository directly.

This makes use of `signedsource` to avoid direct modifications of these
files in the `react-native` repository, as well as `@noformat` and
`@nolint` to prevent unactionable CI failures in that repository.

## How did you test this change?

Generated build files for `react-native` before and after this change:
```
node ./scripts/rollup/build-all-release-channels.js react-native
```

Checked new contents. Relevant changes:

```diff
diff --color -r build-before/react-native/implementations/ReactFabric-dev.fb.js build-after/react-native/implementations/ReactFabric-dev.fb.js
10c10
<  * @generated
---
>  * @generated SignedSource<<03cef14e77b8250b567dfdf3b066085e>>
diff --color -r build-before/react-native/implementations/ReactFabric-dev.js build-after/react-native/implementations/ReactFabric-dev.js
11c11
<  * @generated
---
>  * @generated SignedSource<<e39eed38a363846ca9ee9b59a225683c>>
diff --color -r build-before/react-native/implementations/ReactFabric-prod.fb.js build-after/react-native/implementations/ReactFabric-prod.fb.js
10c10
<  * @generated
---
>  * @generated SignedSource<<f65efcd6a469d5f6fef1ce647e5ec09a>>
diff --color -r build-before/react-native/implementations/ReactFabric-prod.js build-after/react-native/implementations/ReactFabric-prod.js
11c11
<  * @generated
---
>  * @generated SignedSource<<cdd582aa889b1054b2c5faf412622b18>>
diff --color -r build-before/react-native/implementations/ReactFabric-profiling.fb.js build-after/react-native/implementations/ReactFabric-profiling.fb.js
10c10
<  * @generated
---
>  * @generated SignedSource<<81e74849b24f104882bd298f062be0fa>>
diff --color -r build-before/react-native/implementations/ReactFabric-profiling.js build-after/react-native/implementations/ReactFabric-profiling.js
11c11
<  * @generated
---
>  * @generated SignedSource<<c050b7fa1453dc21ac1c5b98146210a8>>
diff --color -r build-before/react-native/implementations/ReactNativeRenderer-dev.fb.js build-after/react-native/implementations/ReactNativeRenderer-dev.fb.js
10c10
<  * @generated
---
>  * @generated SignedSource<<9c03464b489b41c06a065aeba8619263>>
diff --color -r build-before/react-native/implementations/ReactNativeRenderer-dev.js build-after/react-native/implementations/ReactNativeRenderer-dev.js
11c11
<  * @generated
---
>  * @generated SignedSource<<18b34c037544949dcf9b28f945921ba8>>
diff --color -r build-before/react-native/implementations/ReactNativeRenderer-prod.fb.js build-after/react-native/implementations/ReactNativeRenderer-prod.fb.js
10c10
<  * @generated
---
>  * @generated SignedSource<<592e9654c584d1da523378b119bd8bd7>>
diff --color -r build-before/react-native/implementations/ReactNativeRenderer-prod.js build-after/react-native/implementations/ReactNativeRenderer-prod.js
11c11
<  * @generated
---
>  * @generated SignedSource<<91c894db99e2d76f8a32708ad6ad1bde>>
diff --color -r build-before/react-native/implementations/ReactNativeRenderer-profiling.fb.js build-after/react-native/implementations/ReactNativeRenderer-profiling.fb.js
10c10
<  * @generated
---
>  * @generated SignedSource<<5ce378a9216ea747d91b208b9fd1ebd5>>
diff --color -r build-before/react-native/implementations/ReactNativeRenderer-profiling.js build-after/react-native/implementations/ReactNativeRenderer-profiling.js
11c11
<  * @generated
---
>  * @generated SignedSource<<1c7564f446ee83142976035b2884dcfd>>
diff --color -r build-before/react-native/shims/ReactFabric.js build-after/react-native/shims/ReactFabric.js
7c7
<  * @format
---
>  * @noformat
8a9,10
>  * @nolint
>  * @generated SignedSource<<cece19ddbec9f287c995721f49c68977>>
diff --color -r build-before/react-native/shims/ReactFeatureFlags.js build-after/react-native/shims/ReactFeatureFlags.js
7c7
<  * @format
---
>  * @noformat
8a9,10
>  * @nolint
>  * @generated SignedSource<<2881c8e89ef0f73f4cf6612cb518b197>>
diff --color -r build-before/react-native/shims/ReactNative.js build-after/react-native/shims/ReactNative.js
7c7
<  * @format
---
>  * @noformat
8a9,10
>  * @nolint
>  * @generated SignedSource<<0debd6e5a17dc037cb4661315a886de6>>
diff --color -r build-before/react-native/shims/ReactNativeTypes.js build-after/react-native/shims/ReactNativeTypes.js
7c7
<  * @format
---
>  * @noformat
8a9,10
>  * @nolint
>  * @generated SignedSource<<652b117c94307244bcf5e4af18928903>>
diff --color -r build-before/react-native/shims/ReactNativeViewConfigRegistry.js build-after/react-native/shims/ReactNativeViewConfigRegistry.js
7c7
<  * @format
---
>  * @noformat
8a9,10
>  * @nolint
>  * @generated SignedSource<<ce82e8957367bee7d11379ab88e3f7c5>>
diff --color -r build-before/react-native/shims/createReactNativeComponentClass.js build-after/react-native/shims/createReactNativeComponentClass.js
7c7
<  * @format
---
>  * @noformat
8a9,10
>  * @nolint
>  * @generated SignedSource<<ede54ac2fa1b9a09e234cdf098048989>>
```

scripts/rollup/packaging.js

@@ -7,6 +7,7 @@ const {
   readFileSync,
   writeFileSync,
 } = require('fs');
+const path = require('path');
 const Bundles = require('./bundles');
 const {
   asyncCopyTo,
@@ -14,6 +15,7 @@ const {
   asyncExtractTar,
   asyncRimRaf,
 } = require('./utils');
+const {getSigningToken, signFile} = require('signedsource');
 
 const {
   NODE_ES2015,
@@ -134,6 +136,24 @@ async function copyRNShims() {
     require.resolve('react-native-renderer/src/ReactNativeTypes.js'),
     'build/react-native/shims/ReactNativeTypes.js'
   );
+  processGenerated('build/react-native/shims');
+}
+
+function processGenerated(directory) {
+  const files = readdirSync(directory)
+    .filter(dir => dir.endsWith('.js'))
+    .map(file => path.join(directory, file));
+
+  files.forEach(file => {
+    const originalContents = readFileSync(file, 'utf8');
+    const contents = originalContents
+      // Replace {@}format with {@}noformat
+      .replace(/(\n\s*\*\s*)@format\b.*(\n)/, '$1@noformat$2')
+      // Add {@}nolint and {@}generated
+      .replace(' */\n', ` * @nolint\n * ${getSigningToken()}\n */\n`);
+    const signedContents = signFile(contents);
+    writeFileSync(file, signedContents, 'utf8');
+  });
 }
 
 async function copyAllShims() {