fix and test gpu packinfo packet size and direction sets.

...xperimental/communication/UniformGpuFieldPackInfoBase.hpp

src/walberla/codegen/api.py

src/walberla/codegen/communication/pack_infos.py

tests/BasicLbmScenarios/CMakeLists.txt

tests/BasicLbmScenarios/TestBasicLbmScenarios.cpp