test(docs-infra): run tests in random order (and make them pass) (#31527)

This commit updates the necessary config files to run the angular.io and
docs tooling unit tests in random order (and fixes the tests that were
failing due to their dependence on the previous ordered execution).

Besides being a good idea anyway, running tests in random order is the
new [default behavior in jasmine@3.0.0][1], so this commit is in
preparation of upgrading jasmine to the latest version.

[1]: https://github.com/jasmine/jasmine/blob/v3.0.0/release_notes/3.0.md#breaking-changes

PR Close #31527

aio/src/testing/pretty-printer.service.ts

@@ -0,0 +1,13 @@
+// The actual `PrettyPrinter` service has to load `prettify.js`, which (a) is slow and (b) pollutes
+// the global `window` object (which in turn may affect other tests).
+// This is a mock implementation that does not load `prettify.js` and does not pollute the global
+// scope.
+
+import { of } from 'rxjs';
+
+export class MockPrettyPrinter {
+  formatCode(code: string, language?: string, linenums?: number | boolean) {
+    const linenumsStr = (linenums === undefined) ? '' : `, linenums: ${linenums}`;
+    return of(`Formatted code (language: ${language || 'auto'}${linenumsStr}): ${code}`);
+  }
+}