chore(rename): Rename output to distSsr

[Tobbe]

Rename the build output folder to dist/ssr

It used to be dist/server. But "server" is such an ambiguous word now, so it was confusing.

• Is it "server" because this is the only thing that's run on the server? No. The dist/rsc stuff is also run on the server
• Is it "server" because it's run with the "react-server" condition? Well, it kind of is, but what we think of as being run with "react-server" is really what's in dist/rsc.
• Often, when talking in general about RSC people talk about "the server". In fact what they're most likely talking about in that case is "the RSC server", which is actually our standard web server (we use the same server for both RSC and general serving of our web frontend), and that doesn't live in dist/ at all, and absolutely not in dist/server. That server lives in node_modules. When asked for RSC stuff it'll serve files from dist/rsc.

I think dist/ssr is more clear because the stuff in there is used for the client context during the SSR phase, together with the files in dist/rsc for any server components. It's actually much closer to what's in dist/client than anything server-related.