Playground: Better error messages for special SvelteKit modules.

[brunnerh]

If you directly or indirectly import $app/... in the playground, you get an unhelpful error message like:

Error compiling component
Failed to import $app@latest. Are you sure the package exists?

Maybe there could be some filter for these SvelteKit modules to output a more helpful message as suggested by @frederikhors in:

• Strange error in playground svelte#16084

(The main issue is probably that this filter could easily go out of sync with the current implementation when new modules are added.)