Update sveltekit example application to use prerendering

[basaran]

Goals

Prerendering is a major feature of SvelteKit, and keeping it enabled in the examples would help troubleshoot issues better in the future.

Non-Goals

Background

We have an open issue where projects do not compile when prerendering is enabled.

#10339

Proposal

1. Add +layout.ts, enable prerendering.

[basaran]

I can send a PR, please let me know.