Add strong typing to form field names (e.g. in getInputProps, watch)

[rivasd]

Hello! thank you for this fantastic library!

We are using mantine to handle a big form in the application, and I noticed there are no strong typing checks for the many methods that ask a for a field name

function Demo() {
  const form = useForm({
    mode: 'uncontrolled',
    initialValues: {
      email: '',
      termsOfService: false,
    },
  });

  form.watch('emails', ()=>{}) // this should be flagged by Typescript since initialValues are explicitely passed and it's "email", not "emails"
}

I noticed that many other form libraries implement the behavior when an explicit form type or initialValues object is passed. I am by no means an expert but it seems Mantine already has a lot of the typing code necessary.

Would be great, otherwise we'd need to maintain a separate constant object with field names 😄