Function onOpenEncounterChanged

onOpenEncounterChanged(cb: (encounter: Encounter | null) => void): Unsubscribe
Subscribe to the open encounter change event. When the user navigates to an open encounter page, cb is called with the encounter information. When the user navigates away from an open encounter page, cb is called with null.

This also immediately obtains the currently viewed open encounter (or null) and passes it to cb.
Parameters
- cb: (encounter: Encounter | null) => void
  The callback function to be called when the open encounter changes.
Returns Unsubscribe