New structure M_.block_structure.block().bytecode_jacobs_cols_to_sparse

It maps column indices in the Jacobian returned by bytecode MEX in evaluate
mode (which only contains nonzero columns, but also incorporate recursive
variables), into column indices in the sparse representation (which has 3×n
columns for two-boundaries blocks and n columns for one-boundary blocks).
Columns unused in the sparse representation are indicated by a zero.