support `decorators`

[chenjigeng]

Are you submitting a bug report or a feature request?

feature request

What is the expected behavior?

just like react-final-form.

[Freddy03h]

You can by doing this:

const { form } = useForm({ onSubmit });

calculator(form);

[Freddy03h]

Or, regarding https://github.com/final-form/react-final-form/blob/v5.1.0/src/ReactFinalForm.js#L94, maybe more something like that:

useEffect(() => {
  const unsubscribe = calculator(form);
  return () => unsubscribe();
});

and perhaps we can use this useEffect only on mount

useEffect(() => {
  const unsubscribe = calculator(form);
  return () => unsubscribe();
}, []);

[Freddy03h]

or maybe form

useEffect(() => {
  const unsubscribe = calculator(form);
  return () => unsubscribe();
}, [form]);