A small dataset with one row for each of six groups crossed with three
types, so bars stack by Type and each Type facet of a split bar plot has
one bar per Group. Values is positive and shrinks from Alpha to Gamma;
Numbers and Score are signed, leaning positive for Alpha and negative for
Gamma. Used as the default data for plotthis_BarPlotApp() and
plotthis_SplitBarPlotApp().