Issue 5258 - Implement Filter::As<>() method to make working with filters easier from C++ code

compiled/subscription/DownloadableSubscription.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #include "DownloadableSubscription.h"
 
 DownloadableSubscription::DownloadableSubscription(const String& id)
-    : Subscription(Type::DOWNLOADABLE, id), mFixedTitle(false), mLastCheck(0),
+    : Subscription(classType, id), mFixedTitle(false), mLastCheck(0),
       mHardExpiration(0), mSoftExpiration(0), mLastDownload(0), mLastSuccess(0),
       mErrorCount(0), mDataRevision(0), mDownloadCount(0)
 {
   SetTitle(id);
 }
 
 OwnedString DownloadableSubscription::Serialize() const
 {
   OwnedString result(Subscription::Serialize());
   if (mFixedTitle)
@@ skipping 59 matching lines @@
     result.append(u'\n');
   }
   if (mDownloadCount)
   {
     result.append(u"downloadCount="_str);
     result.append(mDownloadCount);
     result.append(u'\n');
   }
   return result;
 }