qt: use exclusive action group in SortMenu

Sorting type is exclusive, but currently it is not indicated as such.

Cherry-picked from !6019. I also wanted to take qt: use theme icon in SortMenu when available (and use ic_fluent_chevron if theme does not provide that as SVG icon engine is expected to be available), but I realized that QIcon can not be colorized which can make it impossible to see (especially with Windows 11 modern style dark and white menus) so for now I do not want to change the icon generation.

Request review @chub.