feat(bazel): add an ng_package rule (#22221)

This produces a directory following the Angular Package layout spec.

Includes integration test coverage by making a minimal ng_package in integration/bazel.
Unit tests verify the content of the @angular/core and @angular/common packages.

This doesn't totally match our current output, but is good enough to unblock some
early adopters.

It re-uses logic from the rollup_bundle rule in rules_nodejs. It should also
eventually have the .pack and .publish secondary targets like npm_package rule.

PR Close #22221

packages/bazel/test/ng_package/common_package.spec.ts

@@ -0,0 +1,50 @@
+/**
+ * @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 * as path from 'path';
+import * as shx from 'shelljs';
+
+shx.cd(path.join(process.env['TEST_SRCDIR'], 'angular', 'packages', 'common', 'npm_package'));
+
+describe('ng_package', () => {
+  it('should have right bundle files', () => {
+    expect(shx.ls('-R', 'bundles').stdout.split('\n').filter(n => !!n).sort()).toEqual([
+      'common-http-testing.umd.js',
+      'common-http-testing.umd.js.map',
+      'common-http-testing.umd.min.js',
+      'common-http-testing.umd.min.js.map',
+      'common-http.umd.js',
+      'common-http.umd.js.map',
+      'common-http.umd.min.js',
+      'common-http.umd.min.js.map',
+      'common-testing.umd.js',
+      'common-testing.umd.js.map',
+      'common-testing.umd.min.js',
+      'common-testing.umd.min.js.map',
+      'common.umd.js',
+      'common.umd.js.map',
+      'common.umd.min.js',
+      'common.umd.min.js.map',
+    ]);
+  });
+  it('should have right fesm files', () => {
+    const expected = [
+      'common.js',
+      'common.js.map',
+      'http',
+      'http.js',
+      'http.js.map',
+      'http/testing.js',
+      'http/testing.js.map',
+      'testing.js',
+      'testing.js.map',
+    ];
+    expect(shx.ls('-R', 'esm5').stdout.split('\n').filter(n => !!n).sort()).toEqual(expected);
+    expect(shx.ls('-R', 'esm2015').stdout.split('\n').filter(n => !!n).sort()).toEqual(expected);
+  });
+});