Summary:
Remove the now useless `handler` and adds the `traversal_func` and `processor`
entries for `std::list`. This type is a bit weird as most of our sequential
containers don't have any overhead on storing the element. I went for the same
approach we take for maps where we have a shared `[]` element covering the map
overhead and below that a `key` & `value`. As we only have a single element
under it which doesn't have a logical name I went for `*`.
Closes#315.
Test Plan:
- CI
- Copied the relevant `std::vector` tests and updated the existing one.
