fix(packages): use ES modules for primary build (#11120)

modules/@angular/platform-server/src/private_export.ts

@@ -0,0 +1,15 @@
+/**
+ * @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 {ClassProvider, ExistingProvider, FactoryProvider, Provider, TypeProvider, ValueProvider} from '@angular/core';
+import {INTERNAL_SERVER_PLATFORM_PROVIDERS} from './server';
+
+export var __platform_server_private__:
+    {INTERNAL_SERVER_PLATFORM_PROVIDERS: typeof INTERNAL_SERVER_PLATFORM_PROVIDERS} = {
+      INTERNAL_SERVER_PLATFORM_PROVIDERS: INTERNAL_SERVER_PLATFORM_PROVIDERS
+    };