[RM-8752] [Vizu] Make generic plot heatmaps mutually exclusive when multiple object types

Created on 2024-03-18 13:56:08 by Thomas Bedrine. % Done: 100

Due to a recent change in "Generic Plot", the density heatmaps are now superposed and hard to read. They should be mutually exclusive, this is very easy to do I've already implemented this on another graph