DataGrid - AI Assistant: Implement message cleanup

[Alyar666]

No description provided.

[Copilot]

Pull request overview

Implements “clear chat” behavior for the DataGrid AI Assistant by wiring the clear-chat UI action to a new AIChat.clear() method and adding unit/integration test coverage to ensure messages are removed.

Changes:

• Added AIChat.clear() to clear the underlying message store and reload the chat’s data source.
• Wired AIAssistantView’s onChatCleared handler to invoke aiChatInstance.clear().
• Added unit tests for AIChat.clear() and AIAssistantView’s handler, plus an integration test validating the UI clears rendered messages.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/devextreme/js/__internal/grids/grid_core/ai_chat/ai_chat.ts	Adds clear() method to remove all chat messages via the data source/store.
packages/devextreme/js/__internal/grids/grid_core/ai_chat/ai_chat.test.ts	Adds unit tests validating clear() behavior and safety when uninitialized.
packages/devextreme/js/__internal/grids/grid_core/ai_assistant/ai_assistant_view.ts	Hooks the clear-chat UI callback to AIChat.clear().
packages/devextreme/js/__internal/grids/grid_core/ai_assistant/tests/ai_assistant_view.test.ts	Adds a unit test ensuring onChatCleared triggers aiChatInstance.clear().
packages/devextreme/js/__internal/grids/grid_core/ai_assistant/tests/ai_assistant_view_controller.integration.test.ts	Adds an integration test that clicking the clear button removes all rendered messages.