MPhys builder needs to initialize MELD with same coordinates upon restart

[Asthelen]

Restarting an MPhys-based aerostructural optimization starting from a different geometry will lead to MELD initialization using the new coordinates, not the baseline design's. This can lead to a slight shift in optimization quantities of interest. A fix is to rerun the baseline design whenever restarting the optimization, but obviously this is inefficient.

I've demoed a solution here (based on @kejacobson's demo a while back): https://github.com/Asthelen/funtofem/tree/mphys_coord_initialization

The idea is to optionally have additional "x_aero0_ref" and "x_struct0_ref" inputs, which will be used to initialize MELD upon restart. These would likely just be connected to the initial mesh coordinates before any geometric deformation.