[staggered][faceVariables] Retrive boundary values in fluxVars
- get the values for parallel and normal velocities directly in the fluxVars and not during the update of the faceVars
- this is necessary in the context of coupling when the velocities on the boundary shall be inferred from the other domain
- the gridFaceVars are initialized (and thus updated) before any coupling context can be bound so this update step must not depend on some coupled context
Edited by Kilian Weishaupt