Make `setTimeout` asynchronous and add `clearTimeout`

[docEdub]

Overview

Improves setTimeout performance by making it asynchronous, and implements clearTimeout.

Details

The current implementation of setTimeout dispatches repeatedly until the given delay is reached. This causes performance issues.

This PR fixes the issue by building on the initial investigative work done in PR https://github.com/BabylonJS/BabylonNative/issues/843 to implement setTimeout asynchronously on a separate thread.

The clearTimeout function is currently not implemented and since it is closely related to setTimeout, it makes sense to implement it in this change, too.

Related tickets

https://github.com/BabylonJS/BabylonNative/issues/253 https://github.com/BabylonJS/BabylonNative/issues/893

[bghgary]

It might also be good to add some unit tests.

[CedricGuillemet]

@docEdub Don't forget to add unit tests here: https://github.com/BabylonJS/BabylonNative/blob/master/Apps/UnitTests/Scripts/tests.js It's handy because it runs on Mac and Linux as well.