feat: support schedulers within run

[cartant]

Description:

In #5607, an animate function was added to the run helpers to enable the testing of the animationFrames observable.

IMO, if we are going to extend the TestScheduler to facilitate the testing of animationFrames, we might as well extend it so that the animateFrameScheduler is testable, too. And if that's done, we might as well make the asapScheduler testable.

This PR adds providers and delegates for set/clearImmediate and set/clearInterval so that schedulers can be supported within TestScheduler#run in a manner similar to the animationFrames observable.

The AsyncScheduler.delegate has been removed, as all delegation now happens via the providers.

This test demonstrates the behaviour of the delegated implementation with the TestScheduler:

it('should support animationFrame, async and asap schedulers', () => {
  const testScheduler = new TestScheduler(assertDeepEquals);
  testScheduler.run(({ animate, cold, expectObservable, time }) => {
    animate('            ---------x');
    const mapped = cold('--m-------');
    const tb = time('      -----|  ');
    const expected = '   --(dc)-b-a';
    const result = mapped.pipe(mergeMap(() => merge(
      of('a').pipe(delay(0, animationFrameScheduler)),
      of('b').pipe(delay(tb, asyncScheduler)),
      of('c').pipe(delay(0, asyncScheduler)),
      of('d').pipe(delay(0, asapScheduler))
    )));
    expectObservable(result).toBe(expected);
  });
});

• asap actions are executed before any async actions on the same marble
• animationFrame actions are executed when specified via the animate helper

A bunch of tests are added to the TestScheduler 'run mode' tests and some of the more high-level AnimationFrameScheduler, AsapScheduler and QueueScheduler tests are replaced with 'run mode'/marble tests.

Related issue (if exists): None

[benlesh]

This is a nice improvement to these tests!

[benlesh]

I think I'll do a follow up to kill the name setImmediate, as that's not really what this does anymore. setImmediate is a failed proposal from back when RxJS 5 was under development 6 years ago. This is really doing microtask scheduling or next tick ..

[benlesh]

Very nice work! Thanks @cartant!