Users can select "Auto" as a filtering option from the image and layer
scaling menus to have Krita pick an appropriate algorithm for them.
This will be the new default selection for both image and layer scaling dialog windows.

We've also added "Auto" as a base option for any KisCmbIDList,
so similar features can be easily added across Krita's GUI.
(Disabled by default. Must set allowAuto(true);)