next.js

0616f1b4 - Add not found boundary and move head cache to app router (#47688)

Add not found boundary and move head cache to app router (#47688) ### What? - Add not found boundary to app router - Move `head` cache back to app router ### Why? We want the head to be rendered separately from body, previously to be able to use `redirect()` and `notFound()` in `generateMetadata` we move the head cache into layout-router to be wrapped by not found and redirect boundaries. Since redirect boudary is already moved to app-router, so we only need to add not found boundary and move head cache to app router. Notice: there's a limitation that we can't find the corresponding not found of page if you throw notFound in generateMetadata, the root layout + root/default not found will be used to generate the 404 page ### How? Closes NEXT-864 Fixes #46738 fix NEXT-888 ([link](https://linear.app/vercel/issue/NEXT-888)) ---------