Better waitFor on scheduler

[dubzzz]

💡 Idea

Currently the scheduler exposes one recommended but hard to use way to wait for something. At the moment, it requires the user to provide a Promise that will keep the scheduler running until it succeeds.

When writing tests, it can be handful to be able to waitFor a predicate to be fulfilled. A waitFor à-la react-testing might probably be a good target: https://testing-library.com/docs/dom-testing-library/api-async/#waitfor

[dubzzz]

Might be cool to have it before the next major, see #3891