update Call Notification
This is called whenever the current Telecom Manager state changes for the app.
Typically your implementation of this will start a persistent notification using Android's NotificationManager
API when the telecom call state is TelecomCall.Registered and dismiss any such notification when the call state is something else.
Create a single instance of this type and set it in the variable callNotificationManager before making any calls.
Parameters
call
The current telecom call state.