deprecate one possible way of using the plotting utility
The original approach was a breaking change, e.g.
dune.fem.plotting.plotPointData(polygons,figure=fig, AttributeError: module 'dune.fem' has no attribute 'plotting' https://gitlab.dune-project.org/dune-fem/dune-vem/-/jobs/519281
It works with from dune.fem.plotting import plotPointData but import dune.fem dune.fem.plotting.plotPointData(...) worked before but now fails with the above AttributeError.
This tries to deprecate that approach but not sure if there are other side effects