Implement sim.output.fields.plot_...

Snek5000 has functions to create figures and movies with 2d cross-sections of the flow.

See for example https://snek5000.readthedocs.io/en/latest/tuto_phill_script.html and the movie in https://github.com/snek5000/snek5000

We want to have the same in fluidsimfoam. We need to reuse code already in fluidsim_core...

See files in https://foss.heptapod.net/fluiddyn/fluidsim/-/tree/branch/default/lib/fluidsim_core/output

Part of the implementation for Snek5000 is actually in fluidsim_core (https://foss.heptapod.net/fluiddyn/fluidsim/-/blob/branch/default/lib/fluidsim_core/output/phys_fields_snek5000.py) and it might be useful to use it for fluidsimfoam.