feat(docs-infra): add shortcuts for the angular.io PWA (angular#40393)

This commits adds some shortcut definitions for the angular.io PWA. The
user agent can use them to assemble a context menu to be displayed by
the operating system when a user engages with the app's icon. (In
addition, shortcuts provide an easy way for users to add links to
specific pages on their home screen.)

See [here][1] for more details on the `shortcuts` property of the PWA
manifest.

The choice of pages to create shortcuts to was influenced by the
following facts/criteria:
- It seems that only the first 4 shortcuts are displayed by Chrome (at
  least on my Android phone).
- Since the PWA is mostly used on mobile, I omitted pages that are less
  likely to be useful for mobile users (such as pages related to CLI).

[1]: https://developer.mozilla.org/en-US/docs/Web/Manifest/shortcuts

PR Close angular#40393

Author: gkalpak

aio/src/pwa-manifest.json

@@ -22,5 +22,31 @@
       "purpose": "maskable"
     }
   ],
-  "start_url": "/?utm_source=homescreen"
+  "start_url": "/?utm_source=homescreen",
+  "shortcuts": [
+    {
+      "name": "Go to API Reference",
+      "short_name": "API",
+      "description": "Go to the Angular API reference page.",
+      "url": "/api?utm_source=homescreen"
+    },
+    {
+      "name": "Go to Glossary",
+      "short_name": "Glossary",
+      "description": "Go to the glossary page: A list of common Angular terms and their explanation.",
+      "url": "/guide/glossary?utm_source=homescreen"
+    },
+    {
+      "name": "Go to Resources",
+      "short_name": "Resources",
+      "description": "Go to the resources page: A list of Angular resouces, such as development tooling, UI libraries, books, courses, community publications, podcasts, etc.",
+      "url": "/resources?utm_source=homescreen"
+    },
+    {
+      "name": "Go to Tutorial: Tour of Heroes",
+      "short_name": "Tutorial",
+      "description": "Go to the \"Tour of Heroes\" tutorial page: Learn how to create your first Angular application.",
+      "url": "/tutorial?utm_source=homescreen"
+    }
+  ]
 }

aio/tests/e2e/src/app.po.ts

@@ -41,7 +41,7 @@ export class SitePage {
 
   async navigateTo(pageUrl: string) {
     // Navigate to the page, disable animations, and wait for Angular.
-    await browser.get(`/${pageUrl}`);
+    await browser.get(`/${pageUrl.replace(/^\//, '')}`);
     await browser.executeScript('document.body.classList.add(\'no-animations\')');
     await browser.waitForAngular();
   }

aio/tests/e2e/src/pwa-manifest.e2e-spec.ts

@@ -0,0 +1,29 @@
+import { PwaManifestPage, PwaShortcutItem } from './pwa-manifest.po';
+
+
+describe('PWA manifest', () => {
+  const page = new PwaManifestPage();
+
+  describe('shortcuts', () => {
+    let shortcuts: PwaShortcutItem[];
+
+    // Helpers
+    const pageExists = async (url: string) => {
+      await page.navigateTo(url);
+      const content = await page.getDocViewerText();
+      return !/page not found/i.test(content);
+    };
+
+    beforeEach(async () => {
+      shortcuts = await page.getPwaShortcuts();
+    });
+
+    it('should exist', async () => {
+      for (const {short_name, url} of shortcuts) {
+        expect(await pageExists(url)).toBe(
+            true,
+            `Page for shortcut '${short_name}' (from '${page.pwaManifestUrl}') does not exist. (URL: ${url})`);
+      }
+    });
+  });
+});

aio/tests/e2e/src/pwa-manifest.po.ts

@@ -0,0 +1,74 @@
+import { get as httpGet } from 'http';
+import { get as httpsGet } from 'https';
+import { browser } from 'protractor';
+import { SitePage } from './app.po';
+
+
+export type Json = null | boolean | number | string | Json[] | { [key: string]: Json };
+
+/**
+ * The shape of a PWA manifest.
+ * For simplicity, we only define types for the properties we care about in tests.
+ * @see https://developer.mozilla.org/en-US/docs/Web/Manifest
+ */
+export type PwaManifest = Json & {
+  shortcuts?: PwaShortcutItem[],
+};
+
+/**
+ * The shape of an item in a PWA manifest's `shortcuts` list.
+ * @see https://developer.mozilla.org/en-US/docs/Web/Manifest/shortcuts
+ */
+export type PwaShortcutItem = Json & {
+  url: string,
+  name: string,
+  short_name?: string,
+  description?: string,
+  icons?: PwaImageResource[],
+};
+
+/**
+ * The shape of an item in a PWA manifest's icons list (such as the value of the top-level `icons` property or that of
+ * the `icons` property of a shortcut item).
+ * @see https://w3c.github.io/manifest/#manifestimageresource-and-its-members
+ */
+export type PwaImageResource = Json & {
+  src: string,
+  sizes?: string,
+  type?: string,
+  purpose?: string,
+};
+
+
+export class PwaManifestPage extends SitePage {
+  /** The base URL with the trailing `/` stripped off (if any). */
+  baseUrl = browser.baseUrl.replace(/\/$/, '');
+
+  /** The URL to the app's PWA manifest. */
+  pwaManifestUrl = `${this.baseUrl}/pwa-manifest.json`;
+
+  private pwaManifestText: string | null = null;
+
+  /** Get the app's PWA manifest as an object. */
+  async getPwaManifest(): Promise<PwaManifest> {
+    if (this.pwaManifestText === null) {
+      const get = /^https:/.test(this.pwaManifestUrl) ? httpsGet : httpGet;
+
+      this.pwaManifestText = await new Promise<string>((resolve, reject) => {
+        let responseText = '';
+        get(this.pwaManifestUrl, res => res
+            .on('data', chunk => responseText += chunk)
+            .on('end', () => resolve(responseText))
+            .on('error', reject));
+      });
+    }
+
+    return JSON.parse(this.pwaManifestText);
+  }
+
+  /** Get a list of PWA shortcuts as extracted from the app's PWA manifest. */
+  async getPwaShortcuts(): Promise<PwaShortcutItem[]> {
+    const {shortcuts = []} = await this.getPwaManifest();
+    return shortcuts;
+  }
+}