build: Add entry point for Ivy language service (#36864)

This commit adds a new entry point for the Ivy version of language
service. The entry point is just a shell for now, implementation will be
added in subsequent PRs.

The Ivy version of language service could be loaded from the NPM package
via `require(@angular/language-service/bundles/ivy.umd.js)`

PR Close #36864

packages/language-service/ivy/language_service.ts

@@ -0,0 +1,17 @@
+/**
+ * @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 * as ts from 'typescript/lib/tsserverlibrary';
+
+export class LanguageService {
+  constructor(private readonly tsLS: ts.LanguageService) {}
+
+  getSemanticDiagnostics(fileName: string): ts.Diagnostic[] {
+    return [];
+  }
+}