[5.7] Add callable docblock to route registrar methods

[patrickbrouwers]

Yesterday I replied on Twitter on an article about tuple/callable route registration that was recently added. However I wasn't completely right that it works. This PR should make it work.

Relevant PR: #24385
Article: https://murze.be/a-better-way-to-register-routes-in-laravel
Tweet: https://twitter.com/patrickbrouwers/status/1062854056522190849

When using Route registration as follows:

Route::get('smth', [SomeController::class, 'methodName']);

(same for typehinted $router - as Registrar/Router)

You can have the benefit of an IDE (tested with PHPStorm) to rename the methodName string automatically whenever you refactor/rename the actual method name.

However, PhpStorm only does this when the parameter is docblocked as callable. This PR adds the callable docblock to the $action param, so auto-refactoring works in IDE's.

Additional suggestion:

Could be an option to drop the Closure docblock, as that's captured with callable already.