withNextInputAutoFocus does not work with nested components

# Description

When using self-closing-tag components to generate text fields in a form, the `withNextInputAutoFocusForm` does not register the generated textInputs and the expected behaviour does not work : pressing "OK" with a textInput focused submits the entire form.

# Steps to reproduce / example

```
const Form = withNextInputAutoFocusForm(View);

export class ReportForm extends PureComponent {
renderForm = ({ values, handleSubmit }: { values: any, handleSubmit: Function }) => {
return (



);
};

render() {
return (

);
}
}
```

```
export class AircraftInformationSection extends PureComponent {
render() {
return (



);
}
}
```

In this case, [getInputs](https://github.com/bamlab/react-native-formik/blob/master/src/withNextInputAutoFocus.js#L12) does not see any children in the props of ``

# Ideas of technical solution
Create a Provider/Consumer system with textFields subscribing to the form.
Add a prop to the form to specify the order of the fields to be focused.