MOM6: *Removed dependence of OBC solutions on external h

  Made a series of 4 separate corrections to calculations at open boundary
points to avoid any dependencies on the values of thicknesses outside of the
domain:
 - Corrected the calculation of the baroclinic pressure anomaly-driven
accelerations due to deflections of the free surface in open boundary conditions
at the end of the barotropic stepping.
 - Corrected the setup of the BT_cont_type at open boundary condition points.
 - Corrected the calculation of face-areas at open boundary condition points for
finding vertically averaged accelerations.
 - Corrected the calculation of the averaged normal velocities in the bottom
boundary layer at open boundary condition points.
  Each of these code changes do change answers in test cases with some types of
open boundary conditions, and the reference solutions for circle_OBCs have been
updated for the combination of these 4 updates.
MOM6 commit NOAA-GFDL/MOM6@993ad0f