Add updated app dir cache handling (#48516)
This adds the discussed updated cache handling for app dir for more fine
grained control over the cached values. Also adds initial
`revalidateTag` and `revalidatePath` exports from `next/server` although
export location may change.
Continuation of https://github.com/vercel/next.js/pull/47720
x-ref: [slack
thread](https://vercel.slack.com/archives/C042LHPJ1NX/p1681404363048459)
