fix(kit): export AdapterUtils type

[jthegedus]

Before submitting the PR, please make sure you do the following

Export AdapterUtils from the root config type file for use in Adapters.

I am updating the Firebase adapter to the latest API and would like to utilise this AdapterUtils types internally.

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with pnpm test and lint the project with pnpm lint

Changesets

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[Rich-Harris]

Thank you. Mind adding a changeset so we can release this?

[jthegedus]

Never used pnpm changeset, hopefully I did that correctly.

[babichjacob]

Never used pnpm changeset, hopefully I did that correctly.

I think you did it right! 🎉

[jthegedus]

Beautiful, thanks all! 🙏