Make sure coop system never consumes permits without actually performing work

[Darksonn]

As initially described in #3493 (comment), it is noted that if the coop system consumes a permit without doing any work, this can cause a deadlock.

One instance of this is found here:

tokio/tokio/src/time/driver/sleep.rs

Lines 216 to 221 in cc97fb8

	let coop = ready!(crate::coop::poll_proceed(cx));
	me.entry.poll_elapsed(cx).map(move |r| {
	coop.made_progress();
	r
	})

This issue tracks finding all such instances, and should not be closed until we are confident that we have fixed all of them.

[jonhoo]

I'm not sure I follow why the indicated code is buggy? The point of the call to made_progress inside of map is to make it so that if progress isn't made, the budget is not consumed. That is, if coop is dropped without made_progress being called, the budget is restored to what it was prior to the call to poll_proceed. So that code looks right to me.

[Darksonn]

I agree. I think the implementation is right.