Specialized dotInterpolate for the efficient calculation of flux fields

e.g. (fvc::interpolate(HbyA) & mesh.Sf()) -> fvc::flux(HbyA)

This removes the need to create an intermediate face-vector field when
computing fluxes which is more efficient, reduces the peak storage and
improved cache coherency in addition to providing a simpler and cleaner
API.

applications/solvers/DNS/dnsFoam/dnsFoam.C

@@ -92,7 +92,7 @@ int main(int argc, char *argv[])
             surfaceScalarField phiHbyA
             (
                 "phiHbyA",
-                (fvc::interpolate(HbyA) & mesh.Sf())
+                fvc::flux(HbyA)
               + rAUf*fvc::ddtCorr(U, phi)
             );