fix: UNINITIALIZED leaking into get

[hmnd]

fixes #17271

I first encountered a permutation of the above issue where navigating from one page to another caused a value related to a remote function to throw Cannot convert a Symbol value to a string.

I found a few separate but related issues:

• UNITITIALIZED was leaking into batch_values. Now, it will be set as undefined in both batch.apply and batch.capture.
• is_dirty should be true for UNINITIALIZEDs to force recomputing.
• signal.v could still also be UNINITIALIZED for async deriveds.

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🦋 Changeset detected

Latest commit: 8250b92

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

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-17373-svelte.vercel.app/

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Playground

pnpm add https://pkg.pr.new/svelte@17373