Draft: Avoid setting XCURSOR_THEME and XCURSOR_SIZE environment variables
XCURSOR_THEME and XCURSOR_SIZE take precedence over other ways to configure the xcursor theme. To make things more complicated, we need to specify different xcursor size depending on whether it's a native wayland client or an x11 client, e.g. 24 for wayland, and 48 for Xwayland clients (if the output has scale factor 2).
Draft: Depends on Qt 6.5 and other necessary changes in startkde helper + plasma-integration.