Breaking change: allow input decks to work for both 2D and 3D

[ecp-warpx]

Breaking change: allow input decks to work for both 2D and 3D

[WeiqunZhang]

I don't think it will break anything. The users are not required to use the new warpx.prob_lo etc. If they don't, there are no changes in behaviors. We could make warpx.* required if that's desired.

[RemiLehe]

Still, it will break things like num_particles_per_cell_each_dim which will now always expect 3 numbers, even in 2D

[WeiqunZhang]

Well, it's easy to maintain backward compatibility for num_particles_per_cell_each_dim.

    num_particles_per_cell_each_dim.clear();
    pp.getarr("num_particles_per_cell_each_dim", num_particles_per_cell_each_dim);
#if (AMREX_SPACEDIM == 2)
    if (num_particles_per_cell_each_dim.size() == 2) {
        num_particles_per_cell_each_dim.resize(3);
        num_particles_per_cell_each_dim[2] = num_particles_per_cell_each_dim[1];
        num_particles_per_cell_each_dim[1] = 1;
    }
#endif

Yes, PlasmaInjector does need to be modified for 2d. But that's case independent of ParmParse.

[RemiLehe]

OK, sounds good. Thanks for the above code suggestion.