We just track it via the preference value itself rather than duplicating that in any other data structure. It's simple enough.
Contributes to issue CURA-6776.
We can reuse our duplicateMaterial function again but in a simpler way. Also finding the preferred material is simpler with our container tree.
However there seems to be a problem with finding the preferred material; it's not finding generic_pla for UM3 and AA0.4 anyway, and then falls back on a random material. This needs to be fixed in the variant node class.
Contributes to issue CURA-6600.
Just like the QualityManagementModel, this class is intended to be used as proxy for the material management page in the preferences. I'm intending to move all relevant pyqtSlots from the material manager into this one. The advantage of this switch is that the material manager had no well-bounded scope and so tended to become a big mess of all sorts of functions. This one has a clear scope: serve as a proxy for the buttons you can press in the preferences screen for materials.
Contributes to issue CURA-6600.
Cast every sorting key to uppercase before doing this. Don't cast to lowercase or there will be problems with characters that don't have lowercase and with Turkish dotted i vs. undotted i.
Fixes#3460.
