[library] Restore lane state in onLayoutChildren()
[library] Rename mPendingItemPosition to mPendingScrollPosition for clarity
[library] Remove unused constant from TWLayoutManager
[library] Restore mPendingScrollOffset in TWLayoutManager
[library] Rename pos argument in fillAfter/fillBefore for clarity
[library] Add protected getters for pending state in TWLayoutManager
[library] Handle layout state moves in onLayoutChildren()