[library] Avoid extra isVertical() calls in TWStaggeredGridLayoutManager
[library] Rename frame argument to childFrame for clarity
[library] Factor out code to compute a child's width and height
[library] Factor out logic to move layout to visible position
[library] Implement moveLayoutToPosition() for TWSpannableGridLayoutManager
[library] Only move layout when not trying restore lanes
[library] Implement moveLayoutToPosition() for TWGridLayoutManager