@angular/core/testing provide `async` test utility, but the name `async` is
confusing with the javascript keyword `async`. And in some test case, if you
want to use both the `async` from `@angular/core/testing` and `async/await`,
you may have to write the code like this.
```typescript
it('test async operations', async(async() => {
const result = await asyncMethod();
expect(result).toEqual('expected');
}));
```
So in this PR, the `async` is renamed to `waitForAsync` and also deprecate `async`.
PR Close#37583
