test: add E2E test for only ES2015 ngcc with differential loading (#15322)

Author: clydin

tests/legacy-cli/e2e/tests/ivy/ngcc-es2015-only.ts

@@ -0,0 +1,14 @@
+
+import { ng } from '../../utils/process';
+import { createProject } from '../../utils/project';
+
+export default async function() {
+  // Create a new project to avoid polluting node modules for other tests
+  await createProject('ivy-project-ngcc', '--enable-ivy');
+
+  const { stderr, stdout } = await ng('build', '--prod');
+
+  if (stdout.includes('as esm5') || stderr.includes('as esm5')) {
+    throw new Error('ngcc should not process ES5 during differential loading builds.');
+  }
+}

yarn.lock

@@ -11280,7 +11280,7 @@ ts-node@^5.0.0:
     source-map-support "^0.5.3"
     yn "^2.0.0"
 
-tslib@^1.10.0:
+tslib@1.10.0, tslib@^1.10.0:
   version "1.10.0"
   resolved "https://registry.yarnpkg.com/tslib/-/tslib-1.10.0.tgz#c3c19f95973fb0a62973fb09d90d961ee43e5c8a"
   integrity sha512-qOebF53frne81cf0S9B41ByenJ3/IuH8yJKngAX35CmiZySA0khhkovshKK+jGCaMnVomla7gVlIcc3EvKPbTQ==