Add `focused` variable to each element of handles

[tuanddd]

Hi @tannerlinsley, I'd like to add a variable (focused) to a handle so that we are able to do this:

{handles.map(({ getHandleProps, focused }) => (
  <button
    {...getHandleProps({
      style: {
        backgroundColor: focused ? "red" : "yellow",
        width: "14px",
        height: "14px",
        outline: "none",
        borderRadius: "100%",
        border: "solid 1px #888"
      }
    })}
  />
))}

Do you think this is a good idea?
Thanks for the lib btw 😄