dillon1000/react

[Scheduler] Re-throw unhandled errors (#19595)

Because `postTask` returns a promise, errors inside a `postTask`
callback result in the promise being rejected.

If we don't catch those errors, then the browser will report an
"Unhandled promise rejection" error. This is a confusing message to see
in the console, because the fact that `postTask` is a promise-based API
is an implementation detail from the perspective of the developer.
"Promise rejection" is a red herring.

On the other hand, if we do catch those errors, then we need to report
the error to the user in some other way.

What we really want is the default error reporting behavior that a
normal, non-Promise browser event gets.

So, we'll re-throw inside `setTimeout`.