BUG: forces: UName entry is not used

Summary

For basic incompressible and compressible simulations, the force function object has not been using a given UName for the devRhoReff computation (affecting the tangential component), but using the U of the latest available step.

In contrast, the pName has always been being used correctly.

Steps to reproduce

Consider any tutorial using the force function object.

Compute the following, and compare the output of integrated forces or force fields:

fieldAverage of force function object using instantaneous U field.
force function object using a given UMean at the end of the simulation; obtain UMean by using fieldAverage.

The results consistently differ within a certain range of decimal points irrespective of initialisation/sampling duration.

Environment information

api      = 2102
patch    = 210414
HEAD     = 5eb48c443a
version  = com
compiler = Clang (system)
         = clang version 9.0.1 
mpi      = SYSTEMOPENMPI
         = mpirun (Open MPI) 1.10.7.0.5e373bf1fd
OS       = Description:     openSUSE Leap 15.1
opts     = linux64ClangDPInt32Opt

Possible fixes

(EP#1224)