fix: ensure redirect used in packages uses the same Redirect instance

[eltigerchino]

fixes #13816

This PR ensures any packages depending on @sveltejs/kit are not externalised so that the instanceof Redirect checks we have works when another package uses our redirect() method.

Thanks to @dominikg and Vitefu, I've followed the example from https://github.com/sveltejs/vite-plugin-svelte/blob/6e338f4a293dd4a1ef29a96f9362f9a7b36524e4/packages/vite-plugin-svelte/src/utils/options.js#L478-L480

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Latest commit: 699ae17

The changes in this PR will be included in the next version bump.

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@sveltejs/kit	Patch

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