refactor(crnl): split the index file (#688)

### Summary

The previous `index.ts` file of `create-react-native-library` was too
long and complicated to maintain. This PR splits the file a bit

### Test plan

1. We have to make sure that the behavior hasn't changed at all. CI
pipeline is the best way to check this.

Author: atlj

packages/create-react-native-library/src/utils/addCodegenBuildScript.ts renamed to packages/create-react-native-library/src/exampleApp/addCodegenBuildScript.ts

@@ -0,0 +1,46 @@
+import assert from 'node:assert';
+import path from 'path';
+import fs from 'fs-extra';
+import type { ExampleApp } from '../input';
+
+export async function getDependencyVersionsFromExampleApp(
+  folder: string,
+  exampleAppType: ExampleApp
+) {
+  const examplePackageJson = await fs.readJSON(
+    path.join(folder, 'example', 'package.json')
+  );
+
+  const react: string = examplePackageJson.dependencies?.react;
+  assert(
+    react !== undefined,
+    "The generated example app doesn't have React installed."
+  );
+  const reactNative: string = examplePackageJson.dependencies?.['react-native'];
+  assert(
+    reactNative !== undefined,
+    "The generated example app doesn't have React Native installed."
+  );
+
+  const devDependencies: Record<string, string> = {
+    react,
+    'react-native': reactNative,
+  };
+
+  if (exampleAppType === 'vanilla') {
+    // React Native doesn't provide the community CLI as a dependency.
+    // We have to get read the version from the example app and put to the root package json
+    const exampleCommunityCLIVersion =
+      examplePackageJson.devDependencies['@react-native-community/cli'];
+    assert(
+      exampleCommunityCLIVersion !== undefined,
+      "The generated example app doesn't have community CLI installed"
+    );
+
+    devDependencies['@react-native-community/cli'] = exampleCommunityCLIVersion;
+  }
+
+  return {
+    devDependencies,
+  };
+}

packages/create-react-native-library/src/exampleApp/dependencies.ts

@@ -1,10 +1,9 @@
 import fs from 'fs-extra';
 import path from 'path';
 import https from 'https';
-import { spawn } from './spawn';
-import sortObjectKeys from './sortObjectKeys';
-
-export type ExampleType = 'vanilla' | 'test-app' | 'expo' | 'none';
+import { spawn } from '../utils/spawn';
+import sortObjectKeys from '../utils/sortObjectKeys';
+import type { ExampleApp } from '../input';
 
 const FILES_TO_DELETE = [
   '__tests__',
@@ -50,7 +49,7 @@ export default async function generateExampleApp({
   bobVersion,
   reactNativeVersion = 'latest',
 }: {
-  type: ExampleType;
+  type: ExampleApp;
   dest: string;
   arch: 'new' | 'mixed' | 'legacy';
   project: {