update clear chat icon

Author: anna-shakhova

packages/devextreme/js/__internal/grids/grid_core/ai_chat/const.ts

@@ -22,4 +22,4 @@ export const CLASSES = {
   aiChatEmptyImage: 'dx-ai-chat-messagelist-empty-image',
 };
 
-export const CLEAR_CHAT_ICON = 'chatdismiss';
+export const CLEAR_CHAT_ICON = 'clearhistory';