Expose routing promises

[ryanflorence]

In order for React Router transitions to compose with React 19 transitions we need to expose the promises from all of our transition functions:

navigate()
submit()
fetcher.submit()
fetcher.load()
revalidator.revalidate()

This way developers can call into React Router from inside a React transition

let [isPending, startTransition] = useTransition()
startTransition(async () => {
  let stuff = await doSomething()
  let more = await fetcher.submit({ stuff }, { method: "post" })
});

[bluefire2121]

Very cool! I guess you can do this as well.

const [isPending, startTransition] = useTransition()
startTransition(async () => {
  const [more, stuff] = await Promise.all([fetcher.submit({ stuff }, { method: "post" }), doSomething()]);
});