Update/sveltekit breaking changes migration

[3daddict]

• [x] Update routes to new format
• [x] Migrate session to new format
• [x] Handle authentication session data
• [x] Update Nav with reactive session data
• [x] Update login and logout functions

References:

• Removing session #5883
• Form actions #6469
• [breaking] error handling rework #6586

[benmccann]

Thank you, but I already have a PR for this: https://github.com/sveltejs/realworld/pull/134

I think we will introduce some new features to SvelteKit to better support moving away from $session, so I have not merged any changes yet

[3daddict]

Sounds good thanks @benmccann looking forward to seeing your implementation. Closing this one if it's not needed.