Use strong enum type for AffineModel

source/Lib/CommonLib/CommonDef.h

source/Lib/CommonLib/ContextModelling.h

source/Lib/CommonLib/InterPrediction.cpp

source/Lib/CommonLib/MotionInfo.h

source/Lib/CommonLib/Unit.cpp

source/Lib/CommonLib/Unit.h

source/Lib/CommonLib/UnitTools.cpp

source/Lib/CommonLib/dtrace_blockstatistics.cpp

source/Lib/DecoderLib/CABACReader.cpp

source/Lib/DecoderLib/DecCu.cpp

source/Lib/EncoderLib/CABACWriter.cpp

source/Lib/EncoderLib/EncCu.cpp

source/Lib/EncoderLib/InterSearch.cpp

source/Lib/EncoderLib/InterSearch.h