Make it possible to get the route name through params

[mpdude]

Assume you can archive BlogPost instances, and you need to use different route names for archived blog posts. For example, the blog_detail route might be at /blog/{slug}, but blog_archived is at /archive/{slug}.

It would be nice if you could still write {{ object_route(post, 'detail') }} in Twig and make the object route figure out whether to use blog_detail or blog_archived.

To make this possible, we could allow to omit the name configuration parameter from @ObjectRoute under the condition that the set of parameters obtained through params contains a _route param. If that is the case, use _route as the route name.

We should fail if either name is provided and a _route is returned, or if neither one is present.

Admittedly, the motivating use case would require that the BlogPost object itself can make the distinction:

@ObjectRoute(type="detail", params={"_route": "routeName"}) -> calls BlogPost::getRouteName()

However, in combination with #12 the full flexibility could be put into the ObjectRoute declaration.