fix(grid): Export IgxHierGridCellComponent #6711

Author: martinesoff

projects/igniteui-angular/src/lib/grids/hierarchical-grid/index.ts

@@ -4,5 +4,6 @@ export * from './hierarchical-grid.component';
 export * from './hierarchical-grid.module';
 export * from './hierarchical-grid-api.service';
 export * from './hierarchical-row.component';
+export * from './hierarchical-cell.component';
 export * from './row-island-api.service';
 export * from './row-island.component';