Typechecking variants

[Rich-Harris]

This extracts part of #5708 into a separate PR, and adds a vite.config.ts to all templates.

As a result of this, the template projects themselves can have configs that are useful for local development within this repo, such as allowing the filesystem access to the Kit source code.

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Tests

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[changeset-bot]

🦋 Changeset detected

Latest commit: 8567dec

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

This PR includes changesets to release 1 package

Name	Type
create-svelte	Patch

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