Update App Route Signature (#48348)
This updates the app route handler signature to be more correct to
prevent the issue with type casting:
```diff
- (request: Request, ctx) => Response
+ (request: NextRequest, ctx) => Promise<Response> | Response
```
This also ensures that the context paramter has the correct types:
```diff
type AppRouteHandlerFnContext = {
- params?: { [param: string]: any }
+ params?: Record<string, string | string[]>
}
```
