Feature Request - Meta Data by Index

You can get the meta data for the whole field array using the `useFieldArray` hook. However, one thing that would be nice would be to get metadata for each index in the field array.

For example in my use case, users can save an individual field array item (the field at an index) rather than the entire field array. Therefore, I want to validate the field array item before allowing the user to save it. This is possible with the `useForm` hook and some extra work, however, it would be more convenient if I could access the metadata for this field array item and therefore receive the valid/invalid props.