No Coarse/Fine Coordinates inside SparsePacks

[pdmullen]

Currently, when creating a SparsePack with PDOpt::Coarse, the coords object inside the pack does not contain the coarse_coords.

When, for example, a downstream code has a user-defined physical BC that is dependent on spatial location and (also) needs to be set on the coarse buffer (when coarse = true in the BC call chain), there is no way to get at these coordinates from the SparsePack.

I guess the same concern above also exists for fine data...

Assigning to myself.