Decoupling finding the solution and animation of a reorder in CellLayout

Adding new functions to CellLayout, two of them return a solution
(calculateReorder, getSimpleReorder) and the other one takes a
solution and animates that solution (void performReorder) and it can
either submit the solution or just show it for a preview.

Right now this two things are done under the same function:
int[] performReorder. The need to separate this two functions is
because to add this functionality b/188081026 which needs to find
soluion without animation and animation solutions that can be
calculated in another place.

Bug: 188081026
Test: atest ReorderWidgets
Change-Id: Ib519d4346f58f9b55aff5008cd3ccbcfe8443d2d