Generalise checking if items are plots in Plotter2D #3788
Description
Coming from a comment by @rozyczko on PR #3758.
TODO item in the _removeSlicerPlots method in Plotter2D.py.
Go through all items and see if they are a plot. The checks done here are not as thorough as GuiUtils.deleteRedundantPlots (which this takes a lot from). Will this cause problems?
The primary concern is the check (plot_data.plot_role == DataRole.ROLE_DELETABLE), as I am unsure of its purpose. The other checks seem to be related to keeping the new plots for that function
TODO: Generalise this and put it in GuiUtils so that we can use it elsewhere