[Feature]: Propogate the box iterator through the *_mass_flux call stack

[johnmauff]

What feature would you like?

In order to facilitate the conversion of the *_mass_flux call stack to AMReX, the box iterator that currently exists in continuity_PPM() should be utilized throughout the *_mass_flux call stack.

Use case

This will greatly simplify the conversion of all the descendants of the *_mass_flux subroutines.

Additional info

This work should be done in the iturbo branch