Fixing DCPSE for subset

src/DCPSE/DCPSE_op/DCPSE_op.hpp

src/DCPSE/DCPSE_op/tests/DCPSE_op_subset_test.cpp

src/DCPSE/Dcpse.hpp

src/DCPSE/SupportBuilder.hpp

src/Matrix/SparseMatrix_petsc.hpp

src/Vector/Vector_petsc.hpp