Is your feature request related to a problem? Please describe.

The google-cloud-firestore Ruby client does not report errors from listen/watch threads.

@schmidt-sebastian commented:

We do need to raise errors as not all backend errors are handled transparently.

Describe the solution you'd like

Other clients in google-cloud-ruby, such as those for debugger, error_reporting, logger, pubsub, etc) do accept on_error callbacks to surface errors from worker threads. (Example: PubSub::Subscriber#on_error). We should add this feature to DocumentListener and QueryListener.

Describe alternatives you've considered

1. Use a mechanism other than callbacks to surface the errors.
2. Make no changes.