Add ability to handle mesh files that don't have center coordinates

[ekluzek]

For meshes with mizuRoute we don't plan to have center coordinates. The meshes are complex with hundreds to thousands of vertices for each cell, so center coordinates aren't useful. We do have HRU Id's (Hydrologic Response Unit identifiers), that are either strings or integers to have an unique identifier for each cell. The HRU Id's are helpful inside of mizuRoute, but may not be useful for the mediator. But, if the history writing needs a unique identifier it might be useful to use it rather than center coordinates.

Technically center coordinates could be calculated for each cell, but they don't tend to be useful at identifying grid cells readily (where HRU Id's are useful), and technically you could have concave cells that nest into each other and have close if not exactly the same nested coordinates (in practice this is unlikely).

Without center coordinates our cases trigger an error at the following point in med_io_mod.F90.

    if (.not. allocated(ownedElemCoords) .and. ndims > 0 .and. nelements > 0) then
       allocate(ownedElemCoords(ndims*nelements))
       allocate(ownedElemCoords_x(ndims*nelements/2))
       allocate(ownedElemCoords_y(ndims*nelements/2))

       call ESMF_MeshGet(mesh, ownedElemCoords=ownedElemCoords, rc=rc)
       if (chkerr(rc,__LINE__,u_FILE_u)) return.   _**<<<<<<<<<<<< Returns here**_

       ownedElemCoords_x = ownedElemCoords(1::2)
       ownedElemCoords_y = ownedElemCoords(2::2)
    end if

There likely are other changes in the code to compensate for the lack of center coordinates. So we need a plan on how to handle this.

[ekluzek]

This might be something we still want. But, for now we are just using mesh files with center coordinates. So we don't need this right now. So I'm marking this as a wontfix. If we decide we need it later we can add it back in or create another issue for it.