fix: suggest running svelte-migrate with latest if migration does not exist

[geoffrich]

Sometimes we forget to add @latest to the svelte-migrate instructions. This PR updates the error for a missing migration to suggest re-running with latest.

Of course, people on older versions won't get this helpful error, but maybe it will be useful eventually.

Related: #11359, #11360

Example of new error:

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Latest commit: dfcfcc0

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svelte-migrate	Patch

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[benmccann]

Can we check the command that was run to see if @latest was specified or does it not see it?

[geoffrich]

I don't think we have access to that -- @latest only tells npx which version of svelte-migrate to use. We could probably check the version in package.json against the latest version in the registry, but that complexity doesn't seem worth it.