getAppData
Retrieves the AppData associated with the given AppInfo.
This function first gets the ViewData for the provided appInfo. If the ViewData is not an instance of AppSideViewData, it returns null. If the ViewData is an instance of AppInfoViewData and its icon is null, it synchronously loads the icon. Finally, it returns the AppData from the AppSideViewData.
Return
The AppData associated with the appInfo, or null if not found or if the ViewData is not of the correct type.