Re #25548

Double clicking workspace now shows Spectrum/Colorfill option
Adds PlotTypeDialog that shows the Spectrum/Colorfill options, then
shows either the Colorfill plot, or the Spectrum dialog.
Add test_spectraselectiondialog, and test_plottypedialog.

Refactored PlotTypeDialog to not contain SpectraSelectionDialog, now it
just creates it anew. Adapted test to new behaviour