Idea: Provide option to have KeyHandler throw an error if not inside a FocusGroup

[dylanpyle]

It looks like we explicitly do nothing in this case right now:
https://github.com/ca-la/react-focused-key-handler/blob/main/src/key-handler/index.tsx#L43

If I'm trying to compose multiple layers of key-handling components under a parent FocusGroup, it would be nice to have some kind of "strict mode" to ensure I don't accidentally render them outside of one later on.