feat: skip server builds for static/SPA type apps

[teemingc]

closes #13217

testing

This PR spins up a Vite dev server to perform analysis and prerendering instead of coupling those processes with the SSR build so that we can skip the SSR build if it's not needed.

Why we can do this: during analysis, we're just reading file exports, it doesn't matter if they're built or not. Meanwhile, if everything is prerendered or if SSR is disabled, we have no use for the SSR build output; we build the client and feed its build output filepaths to the SSR manifest during prerendering. Doing so links to the correct client build output chunks when we save the dev server responses.

TODOS

• make vite preview work without an SSR build
• cleanup

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[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 248d7bc:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/248d7bce4781767aaf7c997b1ad02cf58e0262cb

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16823

[changeset-bot]

🦋 Changeset detected

Latest commit: 248d7bc

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

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Minor

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-16823-svelte.vercel.app/

[ottomated]

Pulled this branch into mine to test cloudflare implications, this is the only thing that caused issues (it seemed to work when I swapped out this conditional to always return get_ssr_vite_server)

[teemingc]

Will probably need to change this later on so that it runs a Vite server with the SSR build output; similar to what I did in a previous PR. This ensures that the adapter Vite plugin stubs are run throughout prerendering