feat: Cloudflare Vite plugin integration

[teemingc]

closes #10496
closes #13692
closes #1712
closes #2963
closes #13300
closes #1519

wip

This PR also removes support for Cloudflare Pages.

• export a fetch handler for adapter-cloudflare
• analysis in workerd
• prerender in workerd
• think about what tests are needed

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Preview: https://svelte-dev-git-preview-kit-15627-svelte.vercel.app/

[handlebauer]

Where is this at? Is there an ETA, of sorts?

[teemingc]

Where is this at? Is there an ETA, of sorts?

As of last weekend, all the SvelteKit tests and the Cloudflare adapter tests are passing. I still need to add new tests to ensure the analysis and prerendering steps of the build step work correctly since they now run in the Cloudflare environment too. Last but not least, the two PRs could do with a review or two.