Add stub for experimental_useFormStatus (#26719)

This wires up, but does not yet implement, an experimental hook called
useFormStatus. The hook is imported from React DOM, not React, because
it represents DOM-specific state — its return type includes FormData as
one of its fields. Other renderers that implement similar methods would
use their own renderer-specific types.

The API is prefixed and only available in the experimental channel.

It can only be used from client (browser, SSR) components, not Server
Components.