fix: correctly handle pathnames found in the _redirects file

[eltigerchino]

closes #9138

We need to add the pathnames found in the Cloudflare _redirects file to the exclude array so that they are handled by Cloudflare Pages rather than the Cloudflare Pages worker. This PR also adds the <redirects> directive so that it can be included manually in the exclude array in _routes.json.

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[benmccann]

I see this method is building a RoutesJSONSpec. Is that a structure that's expected by Cloudflare? If so, could you add a comment in the index.d.ts that points to the relevant Cloudflare docs?

[Rich-Harris]

preview: https://svelte-dev-git-preview-kit-12821-svelte.vercel.app/

this is an automated message

[eltigerchino]

Thanks, that's a good suggestion. I've added a link to the _routes.json documentation.
77dc208 (#12821)

[benmccann]

you might be able to put everything after reading the file into a method like parse_redirects that has a unit test. I get a bit nervous that the adapters keep growing without having any tests

[eltigerchino]

I've added a test but I'm not sure if it's enough. Should I add another one to test the case where the redirects parsing fails?