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/packages/docs-ui/src/components/MainNav/Breadcrumb/index.tsx

@@ -7,7 +7,7 @@ import Link from "next/link"
 import { SidebarItemLink } from "types"
 
 export const MainNavBreadcrumbs = () => {
-  const { currentItems, getActiveItem } = useSidebar()
+  const { currentItems, activeItem } = useSidebar()
   const {
     activeItem: mainNavActiveItem,
     breadcrumbOptions: { showCategories },
@@ -63,7 +63,6 @@ export const MainNavBreadcrumbs = () => {
       )
     }
 
-    const activeItem = getActiveItem()
     if (activeItem && !mainNavActiveItem?.path.endsWith(activeItem.path)) {
       if (
         activeItem.parentItem &&
@@ -83,7 +82,7 @@ export const MainNavBreadcrumbs = () => {
     }
 
     return tempBreadcrumbItems
-  }, [currentItems, getActiveItem])
+  }, [currentItems, activeItem])
 
   return (
     <div