Allow withForm components to accept extending properties

[s-hoff]

Replaces #1268.

This fails:

type Test<T> = {
  defaultValues: T
  fun: (props: { value: T }) => {}
}
const t: Test<{ firstName: string }> =
  {} as Test<{ firstName: string, lastName: string }>

But this works:

type Test2<T> = {
  defaultValues: T,
  fun: <TF extends T = T>(props: { value: TF }) => void
}

const t2: Test2<{ firstName: string }> =
  {} as Test2<{ firstName: string, lastName: string }>

Its probably missing some functions and certainly the other frameworks.

[LeCarbonator]

I've mentioned it on Discord previously, but I should list it here in case a maintainer has comments on it:

Some methods can create behaviour that may be unintended if withForm is extendable. One such example is form.reset().

Even when providing all values in the withForm, since it is a subsection of a form, it will reset fields outside of its scope.

[LeCarbonator]

This feature will be implemented in #1469 . withForm will remain intended for splitting single forms into multiple bits.