fix: take private and public into account for constant_assignment of derived state

[paoloricciuti]

Closes #15273

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🦋 Changeset detected

Latest commit: 9f10d01

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

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svelte	Patch

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Preview: https://svelte-dev-git-preview-svelte-15276-svelte.vercel.app/

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Playground

pnpm add https://pkg.pr.new/svelte@15276