Finite area: curvatureSeparation model does not handle coupled patches

Summary

The algorithm in curvatureSeparation.C#L93 does not handle any coupled-patch fields, resulting in incorrect cosine-angle calculation across faces neighbouring processor patches.

Environment information

api = 2406
HEAD = 791796c6
version = v2406
compiler = Clang (system) version 15.0.7
mpi = SYSTEMOPENMPI = mpirun (Open MPI) 1.10.7.0.5e373bf1fd
OS = Description: openSUSE Leap 15.5
opts = linux64ClangDPInt32Opt