* Allow specifying `void` for component state type parameter.
Per comments on https://github.com/DefinitelyTyped/DefinitelyTyped/pull/8543,
the type parameter for component state was changed to `{}` from `any` for
increased type safety, but prevents specifying (non-functional) stateless
components without having empty state parameters, which seems messy. This
changes the type to `{} | void` to allow this while staying stricter than
`any`.
* Make react tests a bit more strict.
* Rename State -> ComponentState to make it a bit more explicit.
