convert the hexadecimal bytes of apns device token as a string and pass back to react native side

ios/RNFIRMessaging.m

@@ -223,7 +223,13 @@ RCT_EXPORT_METHOD(getInitialNotification:(RCTPromiseResolveBlock)resolve rejecte
 
 RCT_EXPORT_METHOD(getAPNSToken:(RCTPromiseResolveBlock)resolve rejecter:(RCTPromiseRejectBlock)reject)
 {
-    resolve([FIRMessaging messaging].APNSToken);
+    NSData * deviceToken = [FIRMessaging messaging].APNSToken;
+    const char *data = [deviceToken bytes];
+    NSMutableString *token = [NSMutableString string];
+    for (NSUInteger i = 0; i < [deviceToken length]; i++) {
+        [token appendFormat:@"%02.2hhX", data[i]];
+    }
+    resolve([token copy]);
 }
 
 RCT_EXPORT_METHOD(getFCMToken:(RCTPromiseResolveBlock)resolve rejecter:(RCTPromiseRejectBlock)reject)