Use fs.cpSync instead of execSync('cp ... (facebook#43368)

Summary:
Pull Request resolved: facebook#43368

This diff replaces direct invocation of the `cp` command with the platform agnostic `fs.cpSync`.
Changelog: [Internal]

Reviewed By: huntie

Differential Revision: D54634108

fbshipit-source-id: 41fe7b44b6534026ef1b930da85725bf3eb1e7bb

packages/react-native/scripts/codegen/generate-artifacts-executor.js

@@ -465,8 +465,7 @@ function generateCode(outputPath, schemaInfo, includesGeneratedCode, platform) {
   const outputDir =
     reactNativeCoreLibraryOutputPath(libraryName, platform) ?? outputPath;
   fs.mkdirSync(outputDir, {recursive: true});
-  // TODO: Fix this. This will not work on Windows.
-  execSync(`cp -R ${tmpOutputDir}/* "${outputDir}"`);
+  fs.cpSync(tmpOutputDir, outputDir, {recursive: true});
   console.log(`[Codegen] Generated artifacts: ${outputDir}`);
 }