BUG: parallel construct finiteArea fails with arbitrary connections (#2152)

- the case of 'fan-like' processor was previously assumed to be
  rare (see merge-request !487 and issue #2084).

  However, Vaggelis Papoutsis noticed that even fairly normal geometries
  can trigger problems.

- replaced the old patch/patch matching style with a more general
  edge-based synchronisation and matching that appears to handle
  the corner cases inherently. The internal communication overhead
  is essentially unchanged, and the logic is simpler.

src/finiteArea/faMesh/faMesh.H

@@ -197,6 +197,13 @@ class faMesh
         static const int quadricsFit_;
 
 
+    // Data Types
+
+        //- Internal class for managing patch/patch bookkeeping
+        //- during construction
+        class patchTuple;
+
+
     // Private Member Functions
 
         //- No copy construct
@@ -268,8 +275,9 @@ class faMesh
 
     // Helpers
 
-        //- Get the polyPatch pairs for the boundary edges (natural order)
-        List<LabelledItem<edge>> getBoundaryEdgePatchPairs() const;
+        //- Get list of (proc/patchi/patchEdgei) tuple pairs in an
+        //- globally consistent ordering
+        List<Pair<patchTuple>> getBoundaryEdgeConnections() const;
 
         //- Create a single patch
         PtrList<faPatch> createOnePatch
@@ -286,14 +294,6 @@ class faMesh
             const dictionary* defaultPatchDefinition = nullptr
         ) const;
 
-        //- Reorder processor edges using order of the
-        //- neighbour processorPolyPatch
-        void reorderProcEdges
-        (
-            faPatchData& patchDef,
-            const List<LabelledItem<edge>>& bndEdgePatchPairs
-        ) const;
-
 
 public:
 

src/finiteArea/faMesh/faPatches/faPatch/faPatchData.C

@@ -28,6 +28,7 @@ License
 #include "faPatchData.H"
 #include "dictionary.H"
 #include "processorFaPatch.H"
+#include "processorPolyPatch.H"
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
@@ -108,6 +109,24 @@ void Foam::faPatchData::assign(const faPatch& fap)
 }
 
 
+bool Foam::faPatchData::assign_coupled(int ownProci, int neiProci)
+{
+    clear();
+
+    if (ownProci == neiProci)
+    {
+        return false;
+    }
+
+    name_ = processorPolyPatch::newName(ownProci, neiProci);
+    type_ = processorFaPatch::typeName;
+    ownerProcId_ = ownProci;
+    neighProcId_ = neiProci;
+
+    return true;
+}
+
+
 int Foam::faPatchData::matchPatchPair
 (
     const labelPair& patchPair

src/finiteArea/faMesh/faPatches/faPatch/faPatchData.H

@@ -98,6 +98,9 @@ public:
         //- Clear and populate with values from finiteArea patch
         void assign(const faPatch& fap);
 
+        //- Set values consistent with a processor coupling
+        bool assign_coupled(int ownProci, int neiProci);
+
         //- True if owner/neighbour processor ids are non-equal
         bool coupled() const noexcept
         {