dillon1000/react

[Flight] Unify plain Server Component and forwardRef under one function (#28261)

This used to be trivial but it's no longer trivial.

In Fizz and Fiber this is split into renderWithHooks and
finishFunctionComponent since they also support indeterminate
components.

Interestingly thanks to this unification we always call functions with
an arity of 2 which is a bit weird - with the second argument being
undefined in everything except forwardRef and legacy context consumers.

This makes Flight makes the same thing but we could also call it with an
arity of 1.

Since Flight errors early if you try to pass it a ref, and there's no
legacy context, the second arg is always undefined.

The practical change in this PR is that returning a Promise from a
forwardRef now turns it into a lazy. We previously didn't support async
forwardRef since it wasn't supported on the client. However, since
eventually this will be supported by child-as-a-promise it seems fine to
support it.