support jsx transform with fragment

[tatchi]

This is my attempt at fixing https://github.com/reasonml/reason-react/issues/834

[anmonteiro]

Thank you! This is a great catch.

I was wondering whether < key=... > </> was possible but it looks like it isn't: https://react.dev/reference/react/Fragment#caveats

[anmonteiro]

I fixed the transformation. in the jsx runtime, children need to be passed in the props object as {children: ...}