Add app param into callable function

[luwake]

if you sure the callable function has no param,I suggest add the $app as a param to $callable, and then you can create router like this:
`
class ApiRouter
{
public function __invoke(App $app)
{
$app->add(AuthMiddleware::class);

    $app->get('/', function (Request $request, Response $response, $args) {
        $response->getBody()->write('Hello world');
        return $response->withHeader('Content-Type', 'text/html');
    })
    ->setName('api.index');
}

}
and use it in app:
$app->group('/api', ApiRouter::class);
`

[coveralls]

Coverage remained the same at 93.223% when pulling 3e0dd1b on luwake:3.x into 403b798 on slimphp:3.x.

[danopz]

Would you may directly backport #2229?

[akrabat]

Duplicate of #2302