[Flight] Fix reference param type in registerServerReference

[unstubbable]

The reference that is passed into registerServerReference can be a plain function. It does not need to have the three additonal properties of a ServerRefeference. In fact, adding these properties (plus bind) is precisely what registerServerReference does.

[react-sizebot]

Comparing: 6c7b41d...bbc6c29

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	175.90 kB	175.90 kB	=	54.75 kB	54.75 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	177.97 kB	177.97 kB	=	55.39 kB	55.39 kB
facebook-www/ReactDOM-prod.classic.js	=	569.81 kB	569.81 kB	=	100.29 kB	100.29 kB
facebook-www/ReactDOM-prod.modern.js	=	553.67 kB	553.67 kB	=	97.38 kB	97.38 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against bbc6c29

[unstubbable]

I think this is still valid, even with #28343.

[sebmarkbage]

It technically shouldn't even be limited to Functions. It technically should be possible to export any object from a "use server" and pass it back to the server by reference. ServerReferences probably shouldn't even have extra properties and just be a WeakMap.

[sebmarkbage]

There's a static typing thing here that comes into play and is not fully thought out yet. Really types should be enforced at the "use client" / "use server" boundaries so you should not be able to annotate something that is non-serializable as an argument across the boundary. This can be enforced by the list of types we know are allowed to pass.

However, function is not a type that is allowed to pass. So passing an action would be an error. Therefore these exports actually needs to get a special marker type when they're imported so that this type can make them allowed again.

[unstubbable]

Yeah, this was more meant from a framework's/bundler's perspective. When implementing the bundling part that generates the registerServerReference calls I stumbled upon this.