[win] Implement Tablet API switching using Qt6 interfaces
Qt6 has a built-in interface for switching the tablet API. Not only it can now switch WinTab/WinInk, it can also do that on the fly, without restarting the application.
The patch also removes the custom implementation of WinTab and WinInk protocol in Krita using event filters. We have not used these files for more than 5 years, so noone really knows/cares if they do actually work.