Issue 4989 - [emscripten] Move filter class files into a separate directory

compiled/filter/ElemHideBase.cpp

 #include "ElemHideBase.h"
-#include "StringScanner.h"
+#include "../StringScanner.h"
 
 namespace
 {
   void NormalizeWhitespace(DependentString& text, String::size_type& domainsEnd,
       String::size_type& selectorStart)
   {
     // For element hiding filters we only want to remove spaces preceding the
     // selector part. The positions we've determined already have to be adjusted
     // accordingly.
 
@@ skipping 108 matching lines @@
       if (it->second && !it->first.empty())
       {
         if (!result.empty())
           result.append(u',');
         result.append(it->first);
       }
     }
   }
   return result;
 }