Adds the androidX flag to a modules pubspec.yaml template so it is se… (#34066)

This is a small follow up to the previous AndroidX PR: https://github.com/flutter/flutter/pull/31028

This fixes an issue mentioned [here](https://github.com/flutter/flutter/issues/28805) where the androidX flag for a module is not set when creating a new project:

`flutter create --androidx -t module my_flutter`

packages/flutter_tools/templates/module/common/pubspec.yaml.tmpl

@@ -85,5 +85,6 @@ flutter:
   # They also do not have any bearing on your native host application's
   # identifiers, which may be completely independent or the same as these.
   module:
+    androidX: {{androidX}}
     androidPackage: {{androidIdentifier}}
     iosBundleIdentifier: {{iosIdentifier}}

packages/flutter_tools/test/commands/create_test.dart

@@ -421,6 +421,40 @@ void main() {
     expect(actualContents.contains('useAndroidX'), false);
   }, timeout: allowForCreateFlutterProject);
 
+  testUsingContext('androidx app module', () async {
+    Cache.flutterRoot = '../..';
+    when(mockFlutterVersion.frameworkRevision).thenReturn(frameworkRevision);
+    when(mockFlutterVersion.channel).thenReturn(frameworkChannel);
+
+    final CreateCommand command = CreateCommand();
+    final CommandRunner<void> runner = createTestCommandRunner(command);
+
+    await runner.run(<String>['create', '--template=module', '--no-pub', '--androidx', projectDir.path]);
+
+    final FlutterProject project = FlutterProject.fromDirectory(projectDir);
+    expect(
+      project.usesAndroidX,
+      true,
+    );
+  }, timeout: allowForCreateFlutterProject);
+
+  testUsingContext('non androidx app module', () async {
+    Cache.flutterRoot = '../..';
+    when(mockFlutterVersion.frameworkRevision).thenReturn(frameworkRevision);
+    when(mockFlutterVersion.channel).thenReturn(frameworkChannel);
+
+    final CreateCommand command = CreateCommand();
+    final CommandRunner<void> runner = createTestCommandRunner(command);
+
+    await runner.run(<String>['create', '--template=module', '--no-pub', '--no-androidx', projectDir.path]);
+
+    final FlutterProject project = FlutterProject.fromDirectory(projectDir);
+    expect(
+      project.usesAndroidX,
+      false,
+    );
+  }, timeout: allowForCreateFlutterProject);
+
   testUsingContext('androidx plugin project', () async {
     Cache.flutterRoot = '../..';
     when(mockFlutterVersion.frameworkRevision).thenReturn(frameworkRevision);