feat(VirtualizedList): add support for `stick-to-center`

[slvvn]

Hi, currently the VirtualizedList only supports having a scroll behavior of sticking to either sides of the list (start or end). In our case we have a very centered UI, and we would like to have an option to have "centering" behavior of the focused item in the list. This PR contains the addition of the stick-to-center scroll behavior, which at the first/last few items (depending on the item widths) will stay at the same position, and the moment it physically becomes possible to center the current item in the list it will do that. Tried to have minimal impact to the codebase, and added some tests as well. It works perfect in our case using a patch for now. Curious what you think about implementing this into the package too.