#14596 Use #pragma omp parallel for when building corner point grids

The loops were annotated with #pragma omp for, which is a work-sharing construct that does nothing outside an enclosing parallel region. Replace it with #pragma omp parallel for so the cell loops actually run in parallel.

ApplicationLibCode/FileInterface/RifRoffFileTools.cpp

@@ -216,7 +216,7 @@ bool RifRoffFileTools::openGridFile( const QString& fileName, RigEclipseCaseData
         size_t numActiveCells = computeActiveCellMatrixIndex( activeCells );
 
         // Loop over cells and fill them with data
-#pragma omp for
+#pragma omp parallel for
         for ( int gridLocalCellIndex = 0; gridLocalCellIndex < cellCount; ++gridLocalCellIndex )
         {
             RigCell& cell = mainGrid->cell( cellStartIndex + gridLocalCellIndex );