Disallow unknown exports

[Rich-Harris]

Closes #7845, by disallowing all unknown exports. For a minority of apps, this will be a breaking change, which is solved easily by moving the offending exports into a non-route file and importing them.

A related breaking change is that prerendering will fail (whether or not you're actively using prerendering) if modules cannot be imported for analysis at build time (e.g. because a file references a missing variable or something). This is a good thing, and something we should have done before, since it prevents surprising runtime errors.

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Latest commit: c090404

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@sveltejs/kit	Patch

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Name	Status	Preview	Updated
kit	✅ Ready (Inspect)	Visit Preview	Dec 7, 2022 at 10:16AM (UTC)
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