refactor(elements): ng-add schematics (#33723)

This PR brings a couple of changes;
- Removes undeed dependencies in bazel targets such as `//packages/common` & `//packages/core`
- Removes RxJs usage
- Adds `document-register-element` to architect test targets
- Use @schematics/angular helpers
- Uses the standard `$source": "projectName"` to get the projectName, which is defined in the `schema.json`
- Use workspace writer to update the workspace config

PR Close #33723

packages/elements/schematics/ng-add/index_spec.ts

@@ -7,19 +7,14 @@
  */
 import {SchematicTestRunner, UnitTestTree} from '@angular-devkit/schematics/testing';
 import * as path from 'path';
-import {Observable} from 'rxjs';
-import {concatMap} from 'rxjs/operators';
 
 import {Schema as ElementsOptions} from './schema';
 
-
-const polyfillPath = 'node_modules/document-register-element/build/document-register-element.js';
-
 // tslint:disable:max-line-length
 describe('Elements Schematics', () => {
   const schematicRunner = new SchematicTestRunner(
       '@angular/elements', path.join(__dirname, '../test-collection.json'), );
-  const defaultOptions: ElementsOptions = {project: 'bar', skipPackageJson: false};
+  const defaultOptions: ElementsOptions = {project: 'elements', skipPackageJson: false};
 
   let appTree: UnitTestTree;
 
@@ -40,20 +35,29 @@ describe('Elements Schematics', () => {
     skipTests: false,
   };
 
-  beforeEach((done) => {
-    schematicRunner.runExternalSchematicAsync('@schematics/angular', 'workspace', workspaceOptions)
-        .pipe(concatMap(
-            (tree) => schematicRunner.runExternalSchematicAsync(
-                '@schematics/angular', 'application', appOptions, tree)))
-        .subscribe((tree: UnitTestTree) => appTree = tree, done.fail, done);
+  beforeEach(async() => {
+    appTree = await schematicRunner
+                  .runExternalSchematicAsync('@schematics/angular', 'workspace', workspaceOptions)
+                  .toPromise();
+    appTree =
+        await schematicRunner
+            .runExternalSchematicAsync('@schematics/angular', 'application', appOptions, appTree)
+            .toPromise();
   });
 
   it('should run the ng-add schematic', async() => {
     const tree =
         await schematicRunner.runSchematicAsync('ng-add', defaultOptions, appTree).toPromise();
-    const configText = tree.readContent('/angular.json');
-    const config = JSON.parse(configText);
-    const scripts = config.projects.elements.architect.build.options.scripts;
-    expect(scripts[0].input).toEqual(polyfillPath);
+    expect(tree.readContent('/projects/elements/src/polyfills.ts'))
+        .toContain(`import 'document-register-element';`);
+  });
+
+  it('should add polyfill as a dependency in package.json', async() => {
+    const tree =
+        await schematicRunner.runSchematicAsync('ng-add', defaultOptions, appTree).toPromise();
+    const pkgJsonText = tree.readContent('/package.json');
+    const pkgJson = JSON.parse(pkgJsonText);
+    const {dependencies} = pkgJson;
+    expect(dependencies['document-register-element']).toBeDefined();
   });
 });