Update TypeScript API Route example (#44517)

The existing example causes issues with eslint's `eslintimport/no-anonymous-default-export` rule that come pre-enabled with `create-next-app`.

Added a name to the api handler function before setting it as the default export.



## Documentation / Examples

- [x] Make sure the linting passes by running `pnpm build && pnpm lint`
- [x] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)


Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>

docs/basic-features/typescript.md

@@ -103,7 +103,7 @@ The following is an example of how to use the built-in types for API routes:
 ```ts
 import type { NextApiRequest, NextApiResponse } from 'next'
 
-export default (req: NextApiRequest, res: NextApiResponse) => {
+export default function handler(req: NextApiRequest, res: NextApiResponse) {
   res.status(200).json({ name: 'John Doe' })
 }
 ```
@@ -117,7 +117,10 @@ type Data = {
   name: string
 }
 
-export default (req: NextApiRequest, res: NextApiResponse<Data>) => {
+export default function handler(
+  req: NextApiRequest,
+  res: NextApiResponse<Data>
+) {
   res.status(200).json({ name: 'John Doe' })
 }
 ```