[PL/CT] Output medium property porosity
With the change of this pull request, the porosity is written to the time-serial vtu
files in the case that the tag chemically_induced_porosity_change
is flagged on.
With the change of this pull request, the porosity is written to the time-serial vtu
files in the case that the tag chemically_induced_porosity_change
is flagged on.