Issue 4125 - [emscripten] Convert filter classes to C++

compiled/ElemHideBase.h

 #pragma once
 
 #include <cstddef>
 
 #include "ActiveFilter.h"
 
 struct ElemHideBaseData
 {
   String::size_type mDomainsEnd;
   String::size_type mSelectorStart;
@@ skipping 24 matching lines @@
   }
 };
 
 struct ElemHideData;
 
 class ElemHideBase : public ActiveFilter
 {
 protected:
   ElemHideBaseData mData;
 public:
-  ElemHideBase(Type type, const String& text, const ElemHideBaseData& data);
+  explicit ElemHideBase(Type type, const String& text, const ElemHideBaseData& data);
   static Type Parse(DependentString& text, ElemHideData& data);
 
   EMSCRIPTEN_KEEPALIVE const DependentString GetSelector() const
   {
     return mData.GetSelector(mText);
   }
 
   EMSCRIPTEN_KEEPALIVE OwnedString GetSelectorDomain() const;
 };