fix(bazel): flat module misses AMD module name on windows (#27839)

* Fixes that the flat module out files do not have a proper AMD module name on Windows. This is currently blocking serving a `ng_module` using the Bazel TypeScript `devserver` on Windows.

PR Close #27839

packages/bazel/test/ngc-wrapped/flat_module_test.ts

@@ -0,0 +1,40 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {obsoleteInIvy, onlyInIvy} from '@angular/private/testing';
+import {existsSync, readFileSync} from 'fs';
+import {dirname, join} from 'path';
+
+describe('flat_module ng_module', () => {
+
+  let packageOutput: string;
+  let flatModuleOutFile: string;
+
+  beforeAll(() => {
+    packageOutput =
+        dirname(require.resolve('angular/packages/bazel/test/ngc-wrapped/flat_module/index.js'));
+    flatModuleOutFile = join(packageOutput, 'flat_module.js');
+  });
+
+  it('should have a flat module out file',
+     () => { expect(existsSync(flatModuleOutFile)).toBe(true); });
+
+  describe('flat module out file', () => {
+
+    obsoleteInIvy('Ngtsc computes the AMD module name differently than NGC')
+        .it('should have a proper AMD module name', () => {
+          expect(readFileSync(flatModuleOutFile, 'utf8'))
+              .toContain(`define("flat_module/flat_module"`);
+        });
+
+    onlyInIvy('Ngtsc computes the AMD module name differently than NGC')
+        .it('should have a proper AMD module name', () => {
+          expect(readFileSync(flatModuleOutFile, 'utf8')).toContain(`define("flat_module"`);
+        });
+  });
+});