ENH: separate registry and revised file locations for finite-area

- The internal storage location of finite-area changes from being
  piggybacked on the polyMesh registry to a having its own dedicated
  registry:

  * allows a clearer separation of field types without name clashes.
  * prerequisite for supporting multiple finite-area regions (future)

Old Locations:
```
   0/Us
   constant/faMesh
   system/faMeshDefinition
   system/faSchemes
   system/faSolution
```

New Locations:
```
   0/finite-area/Us
   constant/finite-area/faMesh
   system/finite-area/faMeshDefinition  (or system/faMeshDefinition)
   system/finite-area/faSchemes
   system/finite-area/faSolution
```

NOTES:
    The new locations represent a hard change (breaking change) that
    is normally to be avoided, but seamless compatibility handling
    within the code was found to be unworkable.

    The `foamUpgradeFiniteArea` script provides assistance with migration.

    As a convenience, the system/faMeshDefinition location continues
    to be supported (may be deprecated in the future).

applications/utilities/parallelProcessing/reconstructPar/reconstructPar.C

@@ -382,9 +382,25 @@ int main(int argc, char *argv[])
             IOobjectList objects
             (
                 procMeshes.meshes()[0],
-                databases[0].timeName()
+                databases[0].timeName(),
+                IOobjectOption::NO_REGISTER
             );
 
+            IOobjectList faObjects;
+
+            if (doFiniteArea && doFields)
+            {
+                // List of area mesh objects (assuming single region)
+                // - scan on processor0
+                faObjects = IOobjectList
+                (
+                    procMeshes.meshes()[0],
+                    databases[0].timeName(),
+                    faMesh::dbDir(word::null),  // local relative to mesh
+                    IOobjectOption::NO_REGISTER
+                );
+            }
+
             if (doFields)
             {
                 // If there are any FV fields, reconstruct them
@@ -545,12 +561,12 @@ int main(int argc, char *argv[])
             }
             else if
             (
-                objects.count<areaScalarField>()
-             || objects.count<areaVectorField>()
-             || objects.count<areaSphericalTensorField>()
-             || objects.count<areaSymmTensorField>()
-             || objects.count<areaTensorField>()
-             || objects.count<edgeScalarField>()
+                faObjects.count<areaScalarField>()
+             || faObjects.count<areaVectorField>()
+             || faObjects.count<areaSphericalTensorField>()
+             || faObjects.count<areaSymmTensorField>()
+             || faObjects.count<areaTensorField>()
+             || faObjects.count<edgeScalarField>()
             )
             {
                 Info << "Reconstructing FA fields" << nl << endl;
@@ -568,7 +584,7 @@ int main(int argc, char *argv[])
                     procFaMeshes.boundaryProcAddressing()
                 );
 
-                reconstructor.reconstructAllFields(objects);
+                reconstructor.reconstructAllFields(faObjects);
             }
             else
             {