refactor: Use readyState instead of the `done` boolean.
refactor: Use readyState instead of the `done` boolean.

Addresses comments here: https://github.com/ReactiveX/rxjs/pull/5661\#discussion_r481786685

benlesh/RxJS,ReactiveX/RxJS,kwonoj/RxJS,kwonoj/RxJS,benlesh/RxJS,martinsik/rxjs,benlesh/RxJS,kwonoj/RxJS,benlesh/RxJS,martinsik/rxjs,martinsik/rxjs,ReactiveX/rxjs,ReactiveX/rxjs,ReactiveX/rxjs,kwonoj/RxJS,ReactiveX/RxJS,ReactiveX/rxjs,ReactiveX/RxJS,martinsik/rxjs,ReactiveX/RxJS