Add prop types of custom components

[bvangraafeiland]

When using the field children, you can pass some props to the Label/Input etc. However, the prop types of the components are JSX.IntrinsicElements['input'] for example, so if you have a custom input component that takes a size prop, you end up with a typescript error.

In reality the props are being passed through, so it will work if you ignore the type error, but it would be nice if the prop types could be merged somehow.