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

compiled/StringScanner.h

+#ifndef ADBLOCK_PLUS_STRING_SCANNER_H
+#define ADBLOCK_PLUS_STRING_SCANNER_H
+
+#include "String.h"
+
+class StringScanner
+{
+private:
+  const String mStr;
+  String::size_type mPos;
+  String::size_type mEnd;
+  String::value_type mTerminator;
+public:
+  StringScanner(const String& str, String::value_type terminator = u'\0')
+      : mStr(str), mPos(0), mEnd(str.length()), mTerminator(terminator) {}
+
+  bool done()
+  {
+    return mPos >= mEnd;
+  }
+
+  String::size_type position()
+  {
+    return mPos - 1;
+  }
+
+  String::value_type next()
+  {
+    String::value_type result = done() ? mTerminator : mStr[mPos];
+    mPos++;
+    return result;
+  }
+};
+
+#endif