Data prop is ignored despite being included in the types

### Are you submitting a **bug report** or a **feature request**?
Feature request, but the types suggest that it might be a bug

### What is the current behavior?
`data` prop is ignored in `useFieldArray` and `FieldArray`

### What is the expected behavior?
`data` prop to be included when registering the field

### Sandbox Link
https://codesandbox.io/s/kind-cartwright-g2kjl?file=/src/App.js

### What's your environment?

final-form@4.20.1
final-form-arrays@3.0.2
react-final-form@6.5.1
react-final-form-arrays@3.1.1