feat: support wrangler.json configuration file in adapter-cloudflare-workers

[linnil1]

closes #13121

The behavior in this PR is a little different from the code in the issue.
Here, the adapter will now also attempt to use wrangler.json if:

• The wrangler.json file exists.
• The config is set to default (wrangler.toml).

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[Rich-Harris]

preview: https://svelte-dev-git-preview-kit-13148-svelte.vercel.app/

this is an automated message

[linnil1]

Related page: https://svelte-dev-git-preview-kit-13148-svelte.vercel.app/docs/kit/adapter-cloudflare-workers

[teemingc]

Thank you!

[teemingc]

Sorry, I was over-eager and forgot to check for a changeset #13151