CellArea.copyContext

This is sometimes needed for cases where rows need to share alignments in one orientation but may be separately grouped in the opposing orientation.

For instance, #GtkIconView creates all icons (rows) to have the same width and the cells theirin to have the same horizontal alignments. However each row of icons may have a separate collective height. #GtkIconView uses this to request the heights of each row based on a context which was already used to request all the row widths that are to be displayed.