illegal server-only module errors are very bad

[Rich-Harris]

Describe the bug

If a universal module/component imports server-only code...

<!-- +page.svelte -->
<script>
  import { getRequestEvent } from '$app/server';
</script>

...you get this error at dev time:

It's annoying that you don't see the import chain until build, and maybe we could fix that. But when you do build, you get this:

There's so much going on here:

• it's the same freaking error, which still says 'try building your app' to get a better error message
• it appears twice — once with a [vite-plugin-sveltekit-compile] [vite-plugin-sveltekit-virtual-modules] prefix, once with only a [vite-plugin-sveltekit-virtual-modules] prefix. Huh?
• it prints the entire file path, instead of one that's relative to your project folder (and hence much more readable)
• it includes a useless noisy stack trace

Separately: if a dependency in node_modules illegally imports a server-only module, you don't find out until build time. Would be nice if there was a way to detect those a bit earlier, though IIUC Vite doesn't give us the necessary metadata. Something to worry about another time, I guess