Add programmatic focus option

[rektdeckard]

Excellent lib! Was thinking it would be nice to be able to programmatically focus a specific element, instead of being at the whims of the layout order. A simple, non-breaking API change could solve this quite nicely, e.g.:

const First = () => {
  // Pass an optional 'id' to useFocus
  const { isFocused } = useFocus({ id: "first" });
  return <Text>{isFocused ? "I am focused" : "I am not focused"}</Text>;
}

const Second = () => {
  // Return a 'focus' function that focuses the element with id matching the argument
  const { isFocused, focus } = useFocus();

  useInput((input) => {
      if (input === "f") focus("first");
    }, { isActive: isFocused }
  );

  return <Text>{isFocused ? "I am focused" : "I am not focused"}</Text>;
}

It looks like the machinery is already there, just not exposed in the API. WDYT?

[vadimdemedes]

This is published in 3.1.0. Thank you, @rektdeckard!