Extension API: Support native dropdown / action menus on StatusBarItem

Currently, a StatusBarItem only accepts a single command. If an extension wants to offer multiple quick actions from a single status bar entry (e.g., a "Dashboard" status bar entry containing quick actions), developers must bind a command that manually calls vscode.window.showQuickPick(). This creates a disconnected modal overlay rather than a native status bar dropup/dropdown menu anchored to the item.

Same reason as in [#332577](https://github.com/microsoft/vscode/issues/332577) i want to create an dashboard that offers multiple actions to one statusbar item so i dont overload the statusbar.

Add native support for attaching a menu contribution or dropdown list directly to a StatusBarItem.
```TypeScript
export interface StatusBarItem {
/**
* An optional array of quick actions or a menu ID to trigger a dropdown from the status bar item.
*/
menu?: vscode.MenuId | { label: string; command: string; args?: any[] }[];
}
```