[Fizz] Move /static build into /server builds (#27327)

This joins the static (prerender) builds with the server builds but
doesn't change the public entry points.

The idea of two separate bundles is that we'd have a specialized build
for Fizz just for the prerender that could do a lot more. However, in
practice the code is implemented with a dynamic check so it's in both.
It's also not a lot of code.

At the same time if you do have a set up that includes both the
prerender and the render in the same build output, this just doubles the
server bundle size for no reason.

So we might as well merge them into one build. However, I don't expose
the `prerender` from `/server`. Instead it's just exposed from the
public `/static` entry point. This leaves us with the option to go back
to separate builds later if it diverges more in the future.