Type children key statically #39
Description
We use currying for ref and key already. There might be some phantom types/GADT things we can use here to statically type the fact that children key exists. More info: https://github.com/reasonml/rehydrate/blob/6808bf1a19e701214e4456967b4aab155d79802c/src/reactRe.re#L60
Alternatively, @jordwalke can take the occasion to design this away without needing fancy types, with his OrderedMap idea (jordan can talk more about this).
The benefit is that this is the last feature we need in order to completely bypass createElement (which sets up the key warning, that we currently piggyback on), and make every JSX render twice faster.