perf(grid): groupBy selection getter filter w/ set instead of array

Author: damyanpetev

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

@@ -278,8 +278,8 @@ export class IgxGridGroupByRowComponent implements OnDestroy {
      * @hidden @internal
      */
     public get selectedRowsInTheGroup(): any[] {
-        const selectedIds = this.gridSelection.filteredSelectedRowIds;
-        return this.groupRow.records.filter(rowID => selectedIds.indexOf(this.getRowID(rowID)) > -1);
+        const selectedIds = new Set(this.gridSelection.filteredSelectedRowIds);
+        return this.groupRow.records.filter(rowID => selectedIds.has(this.getRowID(rowID)));
     }
 
     /**