add class method for getting current app state

- background
- inactive
- active

Author: ianlin

ios/RNVoipPushNotification/RNVoipPushNotificationManager.h

@@ -17,5 +17,6 @@
 - (NSDictionary *)checkPermissions;
 + (void)didUpdatePushCredentials:(PKPushCredentials *)credentials forType:(NSString *)type;
 + (void)didReceiveIncomingPushWithPayload:(PKPushPayload *)payload forType:(NSString *)type;
++ (NSString *)getCurrentAppBackgroundState;
 
 @end

ios/RNVoipPushNotification/RNVoipPushNotificationManager.m

@@ -138,6 +138,11 @@ - (NSDictionary *)checkPermissions
 
 }
 
++ (NSString *)getCurrentAppBackgroundState
+{
+    return RCTCurrentAppBackgroundState();
+}
+
 + (void)didUpdatePushCredentials:(PKPushCredentials *)credentials forType:(NSString *)type
 {
     NSLog(@"[RNVoipPushNotificationManager] didUpdatePushCredentials credentials.token = %@, type = %@", credentials.token, type);