Please gather all stems|bars|histograms|stairs demos in a same Graphics/* section
@sgougeon)
Reported by Samuel GOUGEON (BUG DESCRIPTION:
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The following demos could be gathered in a same Graphics subsection:
* 2D & 3D plots => plot2d3 (stems)
* 2D & 3D plots => histplot
* 2D & 3D plots => hist3d
* Basic functions => Colored histogram
* bar histogram
A stairs demo could be added (polyline_style=2)