Renaming PrefixSum to Scan.

src/TNL/Containers/Algorithms/CudaScanKernel.h

src/TNL/Containers/Algorithms/DistributedScan.h

src/TNL/Containers/Algorithms/Scan.h

src/TNL/Containers/Algorithms/Scan.hpp

src/TNL/Containers/DistributedVector.h

src/TNL/Containers/DistributedVector.hpp

src/TNL/Containers/DistributedVectorView.h

src/TNL/Containers/DistributedVectorView.hpp

src/TNL/Containers/Vector.h

src/TNL/Containers/Vector.hpp

src/TNL/Containers/VectorView.h

src/TNL/Containers/VectorView.hpp

src/TNL/Matrices/BiEllpack_impl.h

src/TNL/Matrices/CSR_impl.h

src/TNL/Matrices/SlicedEllpackSymmetric_impl.h

src/TNL/Matrices/SlicedEllpack_impl.h

src/UnitTests/Containers/DistributedVectorTest.h

src/UnitTests/Containers/VectorPrefixSumTest.h