docs: DX and performance improvements in API reference (#9430)

- Improve scroll behavior between active sections
- Improve lag when clicking on a sidebar item
- Refactor internal working of the `SidebarProvider` to find active items faster.
- Use Next.js's `useRouter` hook for changing the hash (since they added the option to disable scroll)
- Change `isBrowser` from a hook to a provider since it's widely used across applications.
- Other general improvements and fixes.

Closes DOCS-952

www/apps/user-guide/components/Feedback/index.tsx

@@ -15,7 +15,7 @@ type FeedbackProps = Omit<UiFeedbackProps, "event" | "pathName">
 
 const Feedback = (props: FeedbackProps) => {
   const pathname = usePathname()
-  const isBrowser = useIsBrowser()
+  const { isBrowser } = useIsBrowser()
 
   const feedbackPathname = useMemo(() => basePathUrl(pathname), [pathname])
   const reportLink = useMemo(