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);
+  });
+});