message: [ARNotificationsManager] Only register as observer when needed.
diff: RCT_EXPORT_MODULE();
  -- (instancetype)init;
  +- (NSArray<NSString *> *)supportedEvents
  {
  - if ((self = [super init])) {
  - [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(paymentRequestPaidReceived:) name:@"ARPaymentRequestPaid" object:nil];
  + return @[@"PaymentRequestPaid"];
  }
  - return self;
  +
  +// Will be called when this module's first listener is added.
  +-(void)startObserving {
  + [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(paymentRequestPaidReceived:) name:@"ARPaymentRequestPaid" object:nil];
  }
  -- (NSArray<NSString *> *)supportedEvents
  -{
  - return @[@"PaymentRequestPaid"];
  +// Will be called when this module's last listener is removed, or on dealloc.
  +-(void)stopObserving {
  + [[NSNotificationCenter defaultCenter] removeObserver:self name:@"ARPaymentRequestPaid" object:nil];
  }
  - (void)paymentRequestPaidReceived:(NSNotification *)notification
  