Restrict props to `Record`

[natefaubion]

You are guaranteed buggy behavior otherwise.

[coot]

Indeed, we could wrap props in a record like it is dome with the state already. Just limiting to records will rule out newtype wrappers of records (or we could type check this with a type class).

[coot]

We could wait for instance chains in 11.6.0 and use something as simple as this:

class IsRecord a

instance recordIsRecord :: IsRecord {|r}
else instance newtypeRecordIsRecord :: Newtype a {|r} => IsRecord a

[ethul]

Closed by #129