docs(route-handlers): add TS/JS switcher to Route Resolution sect…

…ion in `Route Handlers` (#72222)

This PR fixes issue on the [Route
Handlers](https://nextjs.org/docs/canary/app/building-your-application/routing/route-handlers)
documentation page:

Missing switcher for TS codeblock in [Route
Resolution](https://nextjs.org/docs/canary/app/building-your-application/routing/route-handlers#route-resolution)
section.

![image](https://github.com/user-attachments/assets/9263732d-2852-49a5-a718-1f40a060ee64)

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Co-authored-by: Delba de Oliveira <32464864+delbaoliveira@users.noreply.github.com>

docs/01-app/02-building-your-application/01-routing/13-route-handlers.mdx

@@ -101,7 +101,17 @@ You can consider a `route` the lowest level routing primitive.
 
 Each `route.js` or `page.js` file takes over all HTTP verbs for that route.
 
-```jsx filename="app/page.js"
+```ts filename="app/page.ts" switcher
+export default function Page() {
+  return <h1>Hello, Next.js!</h1>
+}
+
+// ❌ Conflict
+// `app/route.ts`
+export async function POST(request: Request) {}
+```
+
+```js filename="app/page.js" switcher
 export default function Page() {
   return <h1>Hello, Next.js!</h1>
 }