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

compiled/subscription/UserDefinedSubscription.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
@@ skipping 26 matching lines @@
     if (type == Filter::Type::WHITELIST)
       return FilterCategory::WHITELIST;
     if ((type & Filter::Type::ELEMHIDEBASE) == Filter::Type::ELEMHIDEBASE)
       return FilterCategory::ELEMHIDE;
 
     return FilterCategory::NONE;
   }
 }
 
 UserDefinedSubscription::UserDefinedSubscription(const String& id)
-    : Subscription(Type::USERDEFINED, id), mDefaults(0)
+    : Subscription(classType, id), mDefaults(0)
 {
 }
 
 bool UserDefinedSubscription::IsDefaultFor(const Filter& filter) const
 {
   return mDefaults & filterTypeToCategory(filter.mType);
 }
 
 void UserDefinedSubscription::MakeDefaultFor(const Filter& filter)
 {
@@ skipping 37 matching lines @@
     if (mDefaults & FilterCategory::BLOCKING)
       result.append(u" blocking"_str);
     if (mDefaults & FilterCategory::WHITELIST)
       result.append(u" whitelist"_str);
     if (mDefaults & FilterCategory::ELEMHIDE)
       result.append(u" elemhide"_str);
     result.append(u'\n');
   }
   return result;
 }