clearer packaging error messages

[ignatiusmb]

Closes #2951

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[changeset-bot]

🦋 Changeset detected

Latest commit: 69ebc4c

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

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[bluwy]

LGTM. With a small question.

[jcalfee]

Thanks .. I followed the help link to packaging and read all of that, but I'm not sure how to disable typescript so I don't need svelte2tsx and typescript.