Generate projects using the new Android embedding (#41666)

* Generate projects using the new Android embedding

* Add comment about usesNewEmbedding:true

* Feedback

* Rework way to detect new embedding in new apps

packages/flutter_tools/lib/src/project.dart

diff --git a/packages/flutter_tools/lib/src/project.dart b/packages/flutter_tools/lib/src/project.dart
index dd5ce15..3b7ad27 100644
--- a/packages/flutter_tools/lib/src/project.dart
+++ b/packages/flutter_tools/lib/src/project.dart
@@ -608,7 +608,11 @@
 
   void _regenerateLibrary() {
     _deleteIfExistsSync(ephemeralDirectory);
-    _overwriteFromTemplate(fs.path.join('module', 'android', 'library'), ephemeralDirectory);
+    _overwriteFromTemplate(fs.path.join(
+      'module',
+      'android',
+      featureFlags.isNewAndroidEmbeddingEnabled ? 'library_new_embedding' : 'library',
+    ), ephemeralDirectory);
     _overwriteFromTemplate(fs.path.join('module', 'android', 'gradle'), ephemeralDirectory);
     gradle.injectGradleWrapperIfNeeded(ephemeralDirectory);
   }
@@ -621,6 +625,7 @@
         'projectName': parent.manifest.appName,
         'androidIdentifier': parent.manifest.androidPackage,
         'androidX': usesAndroidX,
+        'useNewAndroidEmbedding': featureFlags.isNewAndroidEmbeddingEnabled,
       },
       printStatusWhenWriting: false,
       overwriteExisting: true,