cloneElement should show some runtime error with uppercase components

[jchavarri]

Currently cloneElement is not compatible with uppercase components because unlike in JavaScript, where the props are just a "bag of properties" modelled as a JS object, in server-reason-react a component function takes props as labelled arguments, so it's not possible to "inject" more of these labelled arguments at runtime.

Maybe server-reason-react should warn or show some error when cloneElement is used with uppercase components? Or even hard crash. Otherwise programs might behave in unexpected ways without devs noticing.