Issue 4988 - [emscripten] Adjust API for Element Hiding Emulation filters

compiled/ElemHideBase.h

 #pragma once
 
 #include <cstddef>
 
 #include "ActiveFilter.h"
 
-struct ElemHideBaseData
+struct ElemHideData
 {
   String::size_type mDomainsEnd;
   String::size_type mSelectorStart;
 
   bool HasDomains() const
   {
     return mDomainsEnd != 0;
   }
 
   DependentString GetDomainsSource(String& text) const
@@ skipping 10 matching lines @@
   {
     return DependentString(text, mSelectorStart);
   }
 
   const DependentString GetSelector(const String& text) const
   {
     return DependentString(text, mSelectorStart);
   }
 };
 
-struct ElemHideData;
-
 class ElemHideBase : public ActiveFilter
 {
 protected:
-  ElemHideBaseData mData;
+  ElemHideData mData;
 public:
-  explicit ElemHideBase(Type type, const String& text, const ElemHideBaseData& data);
+  explicit ElemHideBase(Type type, const String& text, const ElemHideData& data);
   static Type Parse(DependentString& text, ElemHideData& data);
 
   EMSCRIPTEN_KEEPALIVE const DependentString GetSelector() const
   {
     return mData.GetSelector(mText);
   }
 
   EMSCRIPTEN_KEEPALIVE OwnedString GetSelectorDomain() const;
 };