Added paginator helper to convert first/after and before/last to offset/limit

[OwlyCode]

This adds a standalone object to help on pagination. Its role is to convert GraphQL arguments from the ConnectionArgs to an offset/limit pair. For instance :

    public function resolveList($args)
    {
        $pagination = new EntityPaginator(function ($offset, $limit) {
            return $this->myRepository->getAll($offset, $limit); // Or Doctrine or whatever
        });
        
        // Make use of the 'first' and 'after' arguments
        return $pagination->forward($args);
    }

All you have to do is provide a callable that fetch the items you need to paginate.

For backward pagination, you have to provide an item count :

return $pagination->backward($args, $this->myRepository->count());

You can also have an automatic mode that detects if you go backward or forward :

return $pagination->auto($args, $this->myRepository->count());

To avoid computing a total that is uneeded for forward pagination, you can provide a callable that will only be resolved when going backward :

return $pagination->auto($args, [$this->myRepository, 'count']);

[mcg-web]

LGTM! Thanks for the contribution @OwlyCode :)

[Nyalab]

👏

[ooflorent]

Damn! This is good.

[ooflorent]

toArgument would be a better name

[mcg-web]

private method we can renames it easily before next release without BC