ENH: write patches as vtkPolyData instead of vtkUnstructuredGrid

- slightly better memory efficiency and file sizes
- consistent with library reader

applications/utilities/postProcessing/dataConversion/foamToVTK/writeFuns.H

@@ -73,13 +73,23 @@ public:
 
     // Write header
 
-        static void writeHeader(std::ostream&, const bool, const string&);
-        static void writeCellDataHeader(std::ostream&, const label, const label);
+        static void writeHeader
+        (
+            std::ostream&,
+            const bool isBinary,
+            const std::string& title
+        );
+        static void writeCellDataHeader
+        (
+            std::ostream&,
+            const label nCells,
+            const label nFields
+        );
         static void writePointDataHeader
         (
             std::ostream&,
-            const label,
-            const label
+            const label nPoints,
+            const label nFields
         );