Server action redirects should allow returning state

[icopp]

Right now, if you redirect from inside a server action, there's no way to return any kind of updated state to the call site. If you use useActionState, this means you can't do any kind of side channel behavior (success notifications, etc) in combination with a redirect unless you work out your own hacky arrangement to check stale state and figure out your own de facto standard for what it means.