Ensure only group children are shown on expand.

Author: MKirova

projects/igniteui-angular/src/lib/grids/pivot-grid/pivot-grid.component.ts

@@ -203,6 +203,13 @@ export class IgxPivotGridComponent extends IgxGridBaseDirective implements OnIni
        const fieldColumn =  parentCols.filter(x => x.header === col.header && !x.columnGroup)[0];
        const groupColumn =  parentCols.filter(x => x.header === col.header && x.columnGroup)[0];
        groupColumn.hidden = newState;
+       if (!groupColumn.hidden) {
+            // column group when shown displays all children, we want to show only groups
+           const fieldChildren =  groupColumn.children.filter(x => !x.columnGroup);
+           fieldChildren.forEach(fieldChild => {
+            fieldChild.hidden = true;
+           });
+       }
        fieldColumn.hidden = !newState;
        if (newState) {
         fieldColumn.headerTemplate = this.headerTemplate;