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

compiled/filter/ActiveFilter.h

 /*
  * 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 38 matching lines @@
   typedef StringSet SitekeySet;
   void ParseDomains(const String& domains, String::value_type separator) const;
   void AddSitekey(const String& sitekey) const;
   virtual DomainMap* GetDomains() const;
   virtual SitekeySet* GetSitekeys() const;
   mutable std::unique_ptr<DomainMap> mDomains;
   mutable std::unique_ptr<SitekeySet> mSitekeys;
 private:
   bool mIgnoreTrailingDot;
 public:
+  static constexpr Type classType = Type::ACTIVE;
   explicit ActiveFilter(Type type, const String& text, bool ignoreTrailingDot);
   FILTER_PROPERTY(bool, mDisabled, FILTER_DISABLED, GetDisabled, SetDisabled);
   FILTER_PROPERTY(unsigned int, mHitCount, FILTER_HITCOUNT,
       GetHitCount, SetHitCount);
   FILTER_PROPERTY(unsigned int, mLastHit, FILTER_LASTHIT,
       GetLastHit, SetLastHit);
   bool BINDINGS_EXPORTED IsActiveOnDomain(DependentString& docDomain,
       const String& sitekey) const;
   bool BINDINGS_EXPORTED IsActiveOnlyOnDomain(DependentString& docDomain) const;
   bool BINDINGS_EXPORTED IsGeneric() const;
   OwnedString BINDINGS_EXPORTED Serialize() const;
 };