feat(sveltekit): Support stable SvelteKit 3 (#25009)

SvelteKit 3 is now stable, so this narrows the peer range to `2.x ||
3.x` and runs the `sveltekit-3` e2e apps against the latest 3.x release
as required tests instead of the optional `next` tag.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>