Determine `LinkedList`'s fate

[apasel422]

Should it implement List? Should we add the following method (and/or a corresponding associated type or associated const) to List?

fn is_random_access(&self) -> bool;

[gilescope]

We expect different implementations to have different performance trade-offs. To me random access would feel like the collection supported the Index trait. It is surprising at the moment that the LinkedList is not a form of List.