The path settings are always quite complex in Shiboken.
In the build dir, we have shiboken6.shibokenmodule.shiboken6.so.
In the install dir, we have shiboken6.shiboken6.so.
- rename shiboken6.so to Shiboken.so
- unify the paths in `build` and `install`
- have one single shiboken import
For compatibility, allow to also do this import
This should go away in version 6.2 .