Fix fetchCache config and On-Demand Revalidate handling (#47803)
This ensures we properly honor the `export const fetchCache` config and
also ensures we properly bypass fetch-cache when an On-Demand
Revalidation is occurring.
The `export const dynamic` handling is not changed here as that was
behaving correctly and should not influence fetch cache handling only
whether a page is prerendered fully or treated as SSR.
Fixes: https://github.com/vercel/next.js/issues/47273
x-ref: [slack
thread](https://vercel.slack.com/archives/C042LHPJ1NX/p1679078572123979)