local spatial alignment isn't cleaned up correctly on network disconnect

[chrisfromwork]

Repro:
Run spectator view on an android device, connect to a hololens device or the editor running as the hololens, disrupt the network connection while the marker visual is displaying on device.

Expected:
the marker visual is hidden

Observed:
the marker visual remains/the spatial localization continues to run.

It looks like we complete task completion sources stating that localization has completed, but we don't actually cancel the localization session. To do this we may need to expose some sort of cancel function that can be accessed via the currentLocalizationSession