Adding the avility to add icons on multiple CellLayouts on tests.

I needed to change the code so that you can pass the CellX/Y
position to the drag function instead of the pixel coordinates
and we can pass X position bigger than one CellLayout.

Also, I notice that getCellCenter only worked for 1x1 items
so I added the option to specify the widget size.

Fix: 262431878
Test: atest ReorderWidgets#multipleCellLayoutsSimpleReorder
Change-Id: I3b09de770e8f99aa10cae8cea32e7e6bc02c7b8b