test(language-service): Improve integration test (#28168)

The current integration test for language service involves piping the
results of one process to another using Unix pipes.
This makes the test hard to debug, and hard to configure.

This commit refactors the integration test to use regular Jasmine
scaffolding.

More importantly, it tests the way the language service will actually
be installed by end users. Users would not have to add
`@angular/language-service` to the plugins section in tsconfig.json
Instead, all they need to do is install the *extension* from
the VS Code Marketplace and Angular Language Service will be loaded
as a global plugin.

PR Close #28168

integration/language_service_plugin/generate.ts

@@ -0,0 +1,22 @@
+/**
+ * @fileOverview
+ * This file serves as the entry point for generating goldens file for the
+ * language service integration test. It expects each golden file that needs
+ * to be generated to be passed in as command line arguments.
+ * For example, to generate golden file for the 'configure' request, run
+ * `yarn golden configure.json`.
+ * To generate multiple golden files, run
+ * `yarn golden configure.json completionInfo.json`.
+ *
+ * This is different from just running `yarn jasmine test.js` because this
+ * allows passing in arbitrary arguments.
+ */
+
+import Jasmine = require('jasmine');
+
+function main() {
+  const jasmine = new Jasmine({});
+  jasmine.execute(['test.js']);
+}
+
+main()