In the RecyclerView, only the visible part of the RecyclerView is necessary
to be rendered. Thus, not all the flex items need to be measured at first.
This PR makes the flex lines to be calculated only the visible part.

Also this PR removes the support for the order attribute from the FlexboxLayoutManger because calculating the order requires all view to be inflated at least once, which may lead to bad performance if there is a large number of items in the adapter.