[md][ffpm] Reintroduce coupling conditions header for backwards compatibility

dumux/multidomain/boundary/freeflowporousmedium/couplingconditions.hh

+// -*- mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+// vi: set et ts=4 sw=4 sts=4:
+//
+// SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+// SPDX-License-Identifier: GPL-3.0-or-later
+//
+/*!
+ * \file
+ * \ingroup FreeFlowPorousMediumCoupling
+ * \copydoc Dumux::FreeFlowPorousMediumCouplingConditions
+ */
+
+#ifndef DUMUX_MD_FREEFLOW_POROUSMEDIUM_COUPLINGCONDITIONS_HH
+#define DUMUX_MD_FREEFLOW_POROUSMEDIUM_COUPLINGCONDITIONS_HH
+
+#include <dumux/discretization/method.hh>
+
+#include "couplingconditions_staggered_cctpfa.hh"
+
+namespace Dumux {
+
+namespace FreeFlowPorousMediumDetail {
+
+// declaration (specialize for different discretization types)
+template<class MDTraits, class CouplingManager,
+         class DiscFFMomentum = typename MDTraits::template SubDomain<CouplingManager::freeFlowMomentumIndex>::GridGeometry::DiscretizationMethod,
+         class DiscFFMass = typename MDTraits::template SubDomain<CouplingManager::freeFlowMassIndex>::GridGeometry::DiscretizationMethod,
+         class DiscPM = typename MDTraits::template SubDomain<CouplingManager::porousMediumIndex>::GridGeometry::DiscretizationMethod
+         >
+struct FreeFlowPorousMediumCouplingConditionsSelector;
+
+template<class MDTraits, class CouplingManager>
+struct FreeFlowPorousMediumCouplingConditionsSelector<MDTraits, CouplingManager, DiscretizationMethods::FCStaggered, DiscretizationMethods::CCTpfa, DiscretizationMethods::CCTpfa>
+{ using type = FFPMCouplingConditionsStaggeredCCTpfa<MDTraits, CouplingManager>; };
+
+} // end namespace Detail
+
+template<class MDTraits, class CouplingManager>
+using FreeFlowPorousMediumCouplingConditions = typename FreeFlowPorousMediumDetail::FreeFlowPorousMediumCouplingConditionsSelector<MDTraits,CouplingManager>::type;
+
+} // end namespace Dumux
+
+#endif