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/providers/BrowserProvider/index.tsx

@@ -0,0 +1,41 @@
+"use client"
+
+import React, { useContext, useEffect, useState } from "react"
+
+type BrowserContextType = {
+  isBrowser: boolean
+}
+
+const BrowserContext = React.createContext<BrowserContextType | null>(null)
+
+type BrowserProviderProps = {
+  children: React.ReactNode
+}
+
+export const BrowserProvider = ({ children }: BrowserProviderProps) => {
+  const [isBrowser, setIsBrowser] = useState(false)
+
+  useEffect(() => {
+    setIsBrowser(typeof window !== "undefined")
+  }, [])
+
+  return (
+    <BrowserContext.Provider
+      value={{
+        isBrowser,
+      }}
+    >
+      {children}
+    </BrowserContext.Provider>
+  )
+}
+
+export const useIsBrowser = () => {
+  const context = useContext(BrowserContext)
+
+  if (!context) {
+    throw new Error("useIsBrowser must be used within a BrowserProvider")
+  }
+
+  return context
+}