feat(types): export form body types

[replygirl]

exports SuccessBody and ErrorBody so users can cast response bodies

Motivation

I'm using formspree/formspree-react with jaredpalmer/formik. After I submit the form, I need to set any uncaught errors on the Formik:

<Formik
  ...
  onSubmit={async (values, { setErrors }) => {
    const { body } = await handleSubmit(values)
    if (body.errors)
      setErrors(
        body.errors
          .filter((x): x is Required<typeof x> => !!x.field)
          .reduce(
            (acc, cur) => ({
              ...acc,
              [cur.field]: cur.message,
            }),
            {} as Parameters<typeof setErrors>[0]
          )
      )
  }}
>

TypeScript doesn't like when you access a property of body:

Property 'errors' does not exist on type 'SubmissionBody'.
  Property 'errors' does not exist on type 'SuccessBody' (ts.2339)

Right now, you can get around this with a one-liner thanks to type-fest's UnionToIntersection...

const { errors } = (body as Partial<UnionToIntersection<typeof body>>)

...but this isn't perfect—after collapsing the union, body is no longer narrowable to SuccessBody or ErrorBody.

[colevscode]

Ok! One suggestion: perhaps avoid using formspree-react with formik. Since formik has it's own state management, it seems redundant to also track error states with Formspree's useForm hook. Instead it might make sense to create a formspree client in a useEffect and call the submitForm function directly.