chore(ubergen): combine all Rosetta fixtures (#13670)

We need this to have `jsii-rosetta` runs that try to translate READMEs
from submodules not crash (because it can't find the referenced fixture
files).

This is not a correct final state yet, but it makes the build not crash.

Hopefully allows aws/jsii#2712 to be merged.


----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk-lib/.gitignore

@@ -16,4 +16,5 @@ dist
 # Ignore barrel import entry points
 /*.ts
 
-junit.xml
+junit.xml
+rosetta

packages/aws-cdk-lib/.npmignore

@@ -25,3 +25,4 @@ tsconfig.json
 # exclude cdk artifacts
 **/cdk.out
 junit.xml
+rosetta

tools/ubergen/bin/ubergen.ts

@@ -17,6 +17,7 @@ async function main() {
   const libraries = await findLibrariesToPackage(uberPackageJson);
   await verifyDependencies(uberPackageJson, libraries);
   await prepareSourceFiles(libraries, uberPackageJson);
+  await combineRosettaFixtures(libraries);
 }
 
 main().then(
@@ -232,6 +233,25 @@ async function prepareSourceFiles(libraries: readonly LibraryReference[], packag
   console.log('\t🍺 Success!');
 }
 
+async function combineRosettaFixtures(libraries: readonly LibraryReference[]) {
+  console.log('📝 Combining Rosetta fixtures...');
+
+  const uberRosettaDir = path.resolve(LIB_ROOT, '..', 'rosetta');
+  await fs.remove(uberRosettaDir);
+
+  for (const library of libraries) {
+    const packageRosettaDir = path.join(library.root, 'rosetta');
+    if (await fs.pathExists(packageRosettaDir)) {
+      await fs.copy(packageRosettaDir, uberRosettaDir, {
+        overwrite: true,
+        recursive: true,
+      });
+    }
+  }
+
+  console.log('\t🍺 Success!');
+}
+
 async function transformPackage(
   library: LibraryReference,
   uberPackageJson: PackageJson,
@@ -424,6 +444,7 @@ const IGNORED_FILE_NAMES = new Set([
   '.gitignore',
   '.jest.config.js',
   '.jsii',
+  '.npmignore',
   'node_modules',
   'package.json',
   'test',