ENH: update globalIndex::mpiGather to use MPI intrinsic/user types

- add provisional support for selecting MPI_Gatherv
  when merging fields in the surface writers.
  Uses the 'gatherv' keyword [experimental]

BUG: gatherv/scatterv wrappers used the incorrect data type

- incorrectly checked against UPstream_basic_dataType trait instead of
  UPstream_dataType, which resulted in a count mismatch for
  user-defined types (eg, vector, tensor,...).

  This was not visibly active bug, since previous internal uses of
  gatherv were restricted to primitive types.

COMP: make UPstream dataType traits size(...) constexpr

- allows static asserts and/or compile-time selection
  of code based on size(1)

tutorials/incompressible/simpleFoam/squareBend/Allclean

@@ -0,0 +1,11 @@
+#!/bin/sh
+cd "${0%/*}" || exit                                # Run from this directory
+. ${WM_PROJECT_DIR:?}/bin/tools/CleanFunctions      # Tutorial clean functions
+#------------------------------------------------------------------------------
+
+cleanCase0
+
+# Remove surface and features
+rm -rf constant/triSurface
+
+#------------------------------------------------------------------------------

tutorials/incompressible/simpleFoam/squareBend/system/sampling

@@ -49,7 +49,8 @@ __surfaceFieldValue
     {
         default
         {
-            verbose true;
+            verbose  true;
+            //gatherv  true;
         }
     }
 

tutorials/incompressible/simpleFoam/squareBend/system/samplingDebug

@@ -19,6 +19,12 @@ debug
 
     formatOptions
     {
+        default
+        {
+            verbose  true;
+            //gatherv  true;
+        }
+
         ensight
         {
             collateTimes  true;