Fix radioacesstechnology api deprecated for ios 12.0 or newer (#4960)

* update radio access technology for ios 13

* set version check to 12.0

* styled

* change empty check of dict

Author: ddnan

GoogleDataTransport/GDTCORLibrary/GDTCORPlatform.m

@@ -71,7 +71,18 @@ GDTCORNetworkMobileSubtype GDTCORNetworkMobileSubTypeMessage() {
     };
     networkInfo = [[CTTelephonyNetworkInfo alloc] init];
   });
-  NSString *networkCurrentRadioAccessTechnology = networkInfo.currentRadioAccessTechnology;
+  NSString *networkCurrentRadioAccessTechnology;
+  if (@available(iOS 12, *)) {
+    NSDictionary<NSString *, NSString *> *networkCurrentRadioAccessTechnologyDict =
+        networkInfo.serviceCurrentRadioAccessTechnology;
+    if (networkCurrentRadioAccessTechnologyDict.count) {
+      // In iOS 12, multiple radio technologies can be captured. We prefer not particular radio
+      // tech to another, so we'll just return the first value in the dictionary.
+      networkCurrentRadioAccessTechnology = networkCurrentRadioAccessTechnologyDict.allValues[0];
+    }
+  } else {
+    networkCurrentRadioAccessTechnology = networkInfo.currentRadioAccessTechnology;
+  }
   if (networkCurrentRadioAccessTechnology) {
     NSNumber *networkMobileSubtype =
         CTRadioAccessTechnologyToNetworkSubTypeMessage[networkCurrentRadioAccessTechnology];