Add comments for resizeStarted callback

Author: Alyar

packages/devextreme/js/__internal/grids/grid_core/ai_column/m_ai_column_view.ts

@@ -159,6 +159,12 @@ export const columnHeadersViewExtender = (
     this.columnsResizer = this.getController('columnsResizer');
 
     this.columnsResizer.resizeStarted.add(() => {
+      /**
+       * We need to manually close the DropDownMenu button
+       * because the stopPropagation method is called
+       * when the cell resize is initiated.
+       * Calling this method is necessary to fix bug T252661.
+       */
       this.activeDropDownButtonInstance?.close();
     });
   }

packages/devextreme/js/__internal/grids/grid_core/columns_resizing_reordering/m_columns_resizing_reordering.ts

@@ -702,6 +702,10 @@ export class ColumnsResizerViewController extends modules.ViewController {
 
   private _draggingHeaderView!: DraggingHeaderView;
 
+  /**
+   * Fired when column resizing begins.
+   * Used to notify other components (e.g., to close open dropdowns).
+   */
   public resizeStarted!: Callback;
 
   protected callbackNames(): string[] {