test: add systemjs+umd integration test (#14196)

This test ensures the `__esModule` is set on UMD bundles, thus making them compatible with SystemJS@^0.22.3.

Followup from https://github.com/frankwallis/plugin-typescript/issues/185.

PR Close #14196

packages/platform-server/testing/rollup.config.js

@@ -10,6 +10,7 @@ export default {
   entry: '../../../dist/packages-dist/platform-server/@angular/platform-server/testing.es5.js',
   dest: '../../../dist/packages-dist/platform-server/bundles/platform-server-testing.umd.js',
   format: 'umd',
+  exports: 'named',
   moduleName: 'ng.platformServer.testing',
   globals: {
     '@angular/core': 'ng.core',