docs: use Response.json in examples

[Nic-Polumeyv]

#15448 deprecated the json and text helpers but the docs still teach them. Snippets switch to Response.json and new Response, and the surrounding links follow.

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 72a5ed0:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/72a5ed0ef7b2ca7a2480bd5492b42adb38e13258

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16805

[changeset-bot]

⚠️ No Changeset found

Latest commit: 72a5ed0

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.

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-16805-svelte.vercel.app/

[Nic-Polumeyv]

folded into #16804