use queueMicrotask instead of setTimeout in browsers to avoid browser throttling

[jensengar]

Since setTimeout get throttled by browsers and setImmediate doesn't actually exist in any browsers, we should use queueMicrotask which works very similarly to the intention of setImmediate.

I have an app that uses stanza.io which relies on async's priorityQueue. It was found that priorityQueue is getting throttled because of its use of setTimeout(fn, 0). Most browsers support queueMicrotask, but for those who don't, we will fallback.

[djhouseknecht]

For reference:

• Here is the article explaining Chrome's timer throttling
• Here is the stanza repo: https://github.com/legastero/stanza

[jensengar]

@sauravazad thanks for the approval. Is there anyone else who needs to approve this? And who has merge/release rights for this?

[aearly]

I'll merge this later today.

[aearly]

Published in v3.2.1

[jensengar]

Thanks!