chore: bump peer dep version for SvelteKit

[teemingc]

Part of #1247

Removes some TODOs that we wanted to get done for the next adapter major such as ensuring new Kit features are always available by bumping the peer dep and removing workarounds for ambient types not being available (they are now)

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-15494-svelte.vercel.app/

[teemingc]

Temporary change. This will be 3.0.0 later on anyway

[elliott-with-the-longest-name-on-github]

Do you intend to merge this PR now and update it later or are you planning on leaving this PR until right before the 3.0 release?

[teemingc]

I intend to merge it now but I wasn't sure if we could change this to ^3.0.0 already. Can we?

[benmccann]

you can make it ^3.0.0 now. you'll get a peer dependency warning if trying to use with ^3.0.0-next.0 unless you make that in the range but I think that fine. and it's better than it warning that you're not using ^2.31.0, so might as well go ahead and do it now

[elliott-with-the-longest-name-on-github]

Do you intend to merge this PR now and update it later or are you planning on leaving this PR until right before the 3.0 release?