ENH: provide MPI native minOp, maxOp reduce multiple values

- consistent with sumOp

ENH: globalIndex with gatherNonLocal tag, and use leading dispatch tags

- useful for gather/write where the master data can be written
 separately.  Leading vs trailing dispatch tags for more similarity to
 other C++ conventions.

applications/utilities/preProcessing/viewFactorsGen/viewFactorsGen.C

@@ -194,10 +194,15 @@ triSurface triangulate
 
     // CGAL : every processor has whole surface
 
-    globalIndex globalFaceIdx(surface.size(), globalIndex::gatherOnly());
-    globalIndex globalPointIdx
+    const globalIndex globalFaceIdx
     (
-        surface.points().size(), globalIndex::gatherOnly()
+        globalIndex::gatherOnly{},
+        surface.size()
+    );
+    const globalIndex globalPointIdx
+    (
+        globalIndex::gatherOnly{},
+        surface.points().size()
     );
 
     List<labelledTri> globalSurfaceTris(globalFaceIdx.gather(surface));