feat(service-worker): introduce the @angular/service-worker package (#19274)

This service worker is a conceptual derivative of the existing @angular/service-worker maintained at github.com/angular/mobile-toolkit, but has been rewritten to support use across a much wider variety of applications.

Entrypoints include:

@angular/service-worker: a library for use within Angular client apps to communicate with the service worker.
@angular/service-worker/gen: a library for generating ngsw.json files from glob-based SW config files.
@angular/service-worker/ngsw-worker.js: the bundled service worker script itself.
@angular/service-worker/ngsw-cli.js: a CLI tool for generating ngsw.json files from glob-based SW config files.

packages/service-worker/config/test/generator_spec.ts

@@ -0,0 +1,86 @@
+/**
+ * @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 {Generator} from '../src/generator';
+import {MockFilesystem} from '../testing/mock';
+
+export function main() {
+  describe('Generator', () => {
+    it('generates a correct config', (done: DoneFn) => {
+      const fs = new MockFilesystem({
+        '/index.html': 'This is a test',
+        '/foo/test.html': 'Another test',
+        '/ignored/x.html': 'should be ignored',
+      });
+      const gen = new Generator(fs, '/test');
+      const res = gen.process({
+        index: '/index.html',
+        appData: {
+          test: true,
+        },
+        assetGroups: [{
+          name: 'test',
+          resources: {
+            files: [
+              '/**/*.html', '!/ignored/**',
+              //                '/*.html',
+            ],
+            versionedFiles: [],
+            urls: [
+              '/absolute/**',
+              'relative/*.txt',
+            ]
+          }
+        }],
+        dataGroups: [{
+          name: 'other',
+          urls: [
+            '/api/**',
+            'relapi/**',
+          ],
+          cacheConfig: {
+            maxSize: 100,
+            maxAge: '3d',
+            timeout: '1m',
+          }
+        }]
+      });
+      res.then(config => {
+           expect(config).toEqual({
+             'configVersion': 1,
+             'index': '/test/index.html',
+             'appData': {
+               'test': true,
+             },
+             'assetGroups': [{
+               'name': 'test',
+               'installMode': 'prefetch',
+               'updateMode': 'prefetch',
+               'urls': ['/test/index.html', '/test/foo/test.html'],
+               'patterns': ['\\/absolute\\/.*', '\\/test\\/relative\\/[^\\/]+\\.txt']
+             }],
+             'dataGroups': [{
+               'name': 'other',
+               'patterns': ['\\/api\\/.*', '\\/test\\/relapi\\/.*'],
+               'strategy': 'performance',
+               'maxSize': 100,
+               'maxAge': 259200000,
+               'timeoutMs': 60000,
+               'version': 1,
+             }],
+             'hashTable': {
+               '/test/index.html': 'a54d88e06612d820bc3be72877c74f257b561b19',
+               '/test/foo/test.html': '18f6f8eb7b1c23d2bb61bff028b83d867a9e4643'
+             }
+           });
+           done();
+         })
+          .catch(err => done.fail(err));
+    });
+  });
+}