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/api-reference/utils/check-element-in-viewport.ts

@@ -1,11 +1,10 @@
 export default function checkElementInViewport(
   element: Element,
-  percentage = 100,
-  height?: number
+  percentage = 100
 ) {
   const rect = element.getBoundingClientRect()
   const windowHeight: number | undefined =
-    height || window.innerHeight || document.documentElement.clientHeight
+    window.innerHeight || document.documentElement.clientHeight
 
   return !(
     Math.floor(100 - ((rect.top >= 0 ? 0 : rect.top) / +-rect.height) * 100) <