[0.6.x]: Data Getter Support in vue and vue-inertia Forms

[parafeu]

This PR adds support for inputs data getter in vue and vue-inertia Forms.
It's mirroring the functionality of @inertiajs/vue3's useForm.

Example usage :

let dynamicEmail = '[email protected]'
function getData() {
  return { email: dynamicEmail }
}
const form = useForm('post', '/register', getData) 

[timacdonald]

Thanks!