chore: move dev SSRManifest generation

[teemingc]

Cleans up the Vite dev file a bit but most importantly makes the logic reusable for when we want to use it in analysis and prerendering using a Vite dev server

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 34f8a1a:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/34f8a1ade1d2657ec84f7e72a869c872f1695bde

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16965

[changeset-bot]

⚠️ No Changeset found

Latest commit: 34f8a1a

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-16965-svelte.vercel.app/