Report task execution result in onDidEndTask

The event `vscode.tasks.onDidEndTask` doesn't report the status of the task (i.e. succeeded or failed). It would be great if this can be added to be able to take actions based on that. This will be particularly useful if the task has "dependent" tasks that might fail, in this case the event won't fire for the main task, so there has to be a way to know if any given task succeeded/failed in the chain.