Don't reset work loop until stack is unwound

When replaying a suspended function components, we want to reuse the
hooks that were computed during the original render.

Currently we reset the state of the hooks right after the component 
suspends (or throws an error). This is too early because it doesn't 
give us an opportunity to wait for the promise to resolve.

This refactors the work loop to reset the hooks right before unwinding
instead of right after throwing. It doesn't include any other changes
yet, so there should be no observable behavioral change.