ENH: modify fWallFunction for kEpsilonPhitF model

    The k-epsilon-phit-f turbulence closure model for incompressible and
    compressible flows.

    The model is a three-transport-equation linear-eddy-viscosity turbulence
    closure model alongside an elliptic relaxation equation:
      - Turbulent kinetic energy, \c k,
      - Turbulent kinetic energy dissipation rate, \c epsilon,
      - Normalised wall-normal fluctuating velocity scale, \c phit,
      - Elliptic relaxation factor, \c f.

    Reference:
    \verbatim
        Standard model (Tag:LUU):
            Laurence, D. R., Uribe, J. C., & Utyuzhnikov, S. V. (2005).
            A robust formulation of the v2−f model.
            Flow, Turbulence and Combustion, 73(3-4), 169–185.
            DOI:10.1007/s10494-005-1974-8
    \endverbatim

    The default model coefficients are (LUU:Eqs. 19-20):
    \verbatim
        kEpsilonPhitFCoeffs
        {
            Cmu         0.22,    // Turbulent viscosity constant
            Ceps1a      1.4,     // Model constant for epsilon
            Ceps1b      1.0,     // Model constant for epsilon
            Ceps1c      0.05,    // Model constant for epsilon
            Ceps2       1.9,     // Model constant for epsilon
            Cf1         1.4,     // Model constant for f
            Cf2         0.3,     // Model constant for f
            CL          0.25,    // Model constant for L
            Ceta        110.0,   // Model constant for L
            CT          6.0,     // Model constant for T
            sigmaK      1.0,     // Turbulent Prandtl number for k
            sigmaEps    1.3,     // Turbulent Prandtl number for epsilon
            sigmaPhit   1.0,     // Turbulent Prandtl number for phit = sigmaK
        }
    \endverbatim

Note
    The name of the original variable replacing 'v2' is 'phi' (LUU:Eq. 14).
    However, the name 'phi' preexisted in OpenFOAM; therefore, this name was
    replaced by 'phit'