Don't fire JWT invalid listeners multiple times

* Use a string constant `OS_JWT_TOKEN_INVALID` for a jwt token when we internally invalidated it, instead of setting to `nil`.
* OSIdentityModelRepo will not notify user manager when a token has been set to `OS_JWT_TOKEN_INVALID`. The user manager will already be notified of invalidation by executors.

Author: nan-li

iOS_SDK/OneSignalSDK/OneSignalUser/Source/OSIdentityModelRepo.swift

@@ -97,7 +97,8 @@ extension OSIdentityModelRepo: OSModelChangedHandler {
             args.property == OS_JWT_BEARER_TOKEN,
             let model = args.model as? OSIdentityModel,
             let externalId = model.externalId,
-            let token = args.newValue as? String
+            let token = args.newValue as? String,
+            token != OS_JWT_TOKEN_INVALID // Don't notify when token is invalidated internally
         else {
             return
         }

iOS_SDK/OneSignalSDK/OneSignalUser/Source/OneSignalUserManagerImpl.swift

@@ -681,7 +681,13 @@ extension OneSignalUserManagerImpl {
             OneSignalLog.onesignalLog(.LL_ERROR, message: "Unable to find identity model for externalId: \(externalId)")
             return
         }
-        identityModel.jwtBearerToken = nil
+
+        // Return, if the token has already been invalidated
+        guard identityModel.jwtBearerToken != OS_JWT_TOKEN_INVALID else {
+            return
+        }
+
+        identityModel.jwtBearerToken = OS_JWT_TOKEN_INVALID
 
         fireJwtExpired(externalId: externalId)
     }