suzerain: #3012 better warmer

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44248 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: move x(i) and z(k) to *grid

Victor politely pointed out that it's a pain to get global X, Z
collocation point locations from indices.  Move that functionality
from operator_base to specification_grid, and then delegate
to hold the operator_base API constant.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44249 0bd85f0b-c151-43b9-a1e9-27231104551f