Options for [[GridLayout.addCell]].
Where the actor should be placed within the cell box. Defaults to [[GridLayout.defaultCellAlignment]].
The column index, with 0 on the left.
The actor to be placed in the grid cell. Must be parented to the grid root.
The height of this cell for layout purposes. Should include any desired padding.
The row index, with 0 at the top.
The width of this cell for layout purposes. Should include any desired padding.