feat(v7): stabilize advanced routing

[ArmandPhilippot]

Description (required)

Updates docs to stabilize advanced routing. Kinda supersedes #13944

• Cherry-picks changes made in Update v7 upgrade guide changes #13944 to the v7 upgrade guide and the src/app.ts renaming
• Moves experimental-flags/advanced-routing contents to references/modules/astro-fetch.mdx (new), references/modules/astro-hono.mdx (new), guides/routing.mdx, and /en/guides/integrations-guide/cloudflare.mdx.
• Updates the sidebar to remove/add pages
• Removes the experimental-flags/advanced-routing translations
• Adds a redirection

Most of the content comes from experimental-flags/advanced-routing. But I have tweaked/reworded/reorganized some parts for better integration (ie. a more guide/reference style).

Happy to discuss about the organization (e.g. do we want advanced routing to be more visible?). And maybe this requires more changes, I haven't checked everything yet (e.g. Routing reference says "There is no separate routing configuration in Astro." which sounds maybe a bit outdated now).

Questions:

• Should AstroFetchState be documented? I can see this is the public contract / this matches what we describe under FetchState. But doing const state = new FetchState(); returns FetchState (the whole object, with private things) not AstroFetchState. So, I'm not sure how to integrate that.

Related issues & labels (optional)

• Suggested label: 7.0

For Astro version: 7.0. See astro PR #16877.

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Tracked Files

File	Note
en/guides/integrations-guide/cloudflare.mdx	Source changed, localizations will be marked as outdated.
en/guides/routing.mdx	Source changed, localizations will be marked as outdated.
en/guides/upgrade-to/v7.mdx	Localization changed, will be marked as complete.
en/reference/experimental-flags/advanced-routing.mdx	Source removed, will stop being tracked.
en/reference/modules/astro-fetch.mdx	Localization added, will be marked as complete.
en/reference/modules/astro-hono.mdx	Localization added, will be marked as complete.
fr/reference/experimental-flags/advanced-routing.mdx	Localization removed, will be marked as missing.
ko/reference/experimental-flags/advanced-routing.mdx	Localization removed, will be marked as missing.

Warnings reference

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🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.