Fix Interia based `useForm` return types

[Spice-King]

This will give us usable types for useForm for React and Vue 3 when using Inertia. Related to #31, but not dependant on it.

For now, builds will fail for Vue until inertiajs/inertia#1734 is merged and released, but React will work out of the box. If one wants to test it locally, you can manually fix @inertiajs/vue3 for Typescript's particularities by editing @inertiajs/vue3/types/useForm.d.ts to export it's InertiaFormProps.