Pages router (`/pages`) will continue to support React 18 not the React
19 RC. Current thinking is that we'll add support for React 19 in Pages
Router once 19 is stable.
This does not affect App Router (`/app`) which continues to use the
latest React Canary (i.e. React 19).
https://github.com/vercel/next.js/pull/65058 is required reading to
understand the changes in this PR
---------
Co-authored-by: Zack Tanner <[email protected]>
### What
Reland #64716
Removing the Suspense boundary on top of `next/dynamic` by default, make
it as `React.lazy` component with preloading CSS feature.
* Remove `suspense` option in `next/dynamic` since it's already
deprecated for a while
* Remove the default loading in app router implmentation of
`next/dynamic`
### Why
Extra Suspense boundary is causing extra useless rendering. For SSR, it
shouldn't render `loading` by default
Related: #64060
Related: #64687
Closes
[NEXT-3074](https://linear.app/vercel/issue/NEXT-3074/app-router-content-flickering-with-reactcreatecontext-and-nextdynamic)
This is sort of a breaking change, since removing the Suspense boundary
on top of `next/dynamic` by default. If there's error happening in side
the dynamic component you need to wrap an extra Suspense boundary on top
of it
