feat(core): add support for using async/await with Jasmine (#24637)

Example:
```
it('...', await(async() => {
  doSomething();
  await asyncFn();
  doSomethingAfter();
}));
```

PR Close #24637

packages/core/test/testability/jasmine_await_spec.ts

@@ -0,0 +1,31 @@
/**
 * @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 {jasmineAwait} from '../../testing';


describe('await', () => {
  let pass: boolean;
  beforeEach(() => pass = false);
  afterEach(() => expect(pass).toBe(true));

  it('should convert passes', jasmineAwait(async() => { pass = await Promise.resolve(true); }));

  it('should convert failures', (done) => {
    const error = new Error();
    const fakeDone: DoneFn = function() { fail('passed, but should have failed'); } as any;
    fakeDone.fail = function(value: any) {
      expect(value).toBe(error);
      done();
    };
    jasmineAwait(async() => {
      pass = await Promise.resolve(true);
      throw error;
    })(fakeDone);
  });
});

packages/core/testing/src/jasmine_await.ts

@@ -0,0 +1,34 @@
/**
 * @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
 */

/**
 * Converts an `async` function, with `await`, into a function which is compatible with Jasmine test
 * framework.
 *
 * For asynchronous function blocks, Jasmine expects `it` (and friends) to take a function which
 * takes a `done` callback. (Jasmine does not understand functions which return `Promise`.) The
 * `jasmineAwait()` wrapper converts the test function returning `Promise` into a function which
 * Jasmine understands.
 *
 *
 * Example:
 * ```
 * it('...', jasmineAwait(async() => {
 *   doSomething();
 *   await asyncFn();
 *   doSomethingAfter();
 * }));
 * ```
 *
 */
export function jasmineAwait(fn: () => Promise<any>):
    (done: {(): void; fail: (message?: Error | string) => void;}) => void {
  return function(done: {(): void; fail: (message?: Error | string) => void;}) {
    fn().then(done, done.fail);
  };
}

packages/core/testing/src/testing.ts

@@ -13,6 +13,7 @@
 */

export * from './async';
export * from './jasmine_await';
export * from './component_fixture';
export * from './fake_async';
export * from './test_bed';

tools/public_api_guard/core/testing.d.ts

@@ -53,6 +53,11 @@ export declare class InjectSetupWrapper {
    inject(tokens: any[], fn: Function): () => any;
}

export declare function jasmineAwait(fn: () => Promise<any>): (done: {
    (): void;
    fail: (message?: Error | string) => void;
}) => void;

/** @experimental */
export declare type MetadataOverride<T> = {
    add?: Partial<T>;