Revert "Reverted some C++ modernisation."
Revert "Reverted some C++ modernisation."

This reverts commit d529db8384ca0809c1d17c81c9905eadbd04c3b2.

Indeed, those are shared pointers, not raw pointers!

cellml/libcellml,hsorby/libcellml,hsorby/libcellml,MichaelClerx/libcellml,MichaelClerx/libcellml,nickerso/libcellml,hsorby/libcellml,cellml/libcellml,nickerso/libcellml,MichaelClerx/libcellml,nickerso/libcellml,nickerso/libcellml,cellml/libcellml,hsorby/libcellml,cellml/libcellml