kritarunner: Link against a static pykrita library instead of importing the source files

This solves issue 431226, where Krita sometimes fails to build due to missing the ui_info.h or ui_manager.h files when compiling the kritarunner target. These headers are created when the kritapykrita target is built, but since kritarunner doesn't depend on kritapykrita, it's sometimes built first.

This should also make it easier to maintain the build scripts, since less code has to be duplicated accurately and the duplicated code resides in the same file.