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

compiled/StringScanner.h

-#ifndef ADBLOCK_PLUS_STRING_SCANNER_H
-#define ADBLOCK_PLUS_STRING_SCANNER_H
+#pragma once
 
-#include <string>
+#include "String.h"
 
 class StringScanner
 {
 private:
-  const std::u16string str;
-  size_t pos;
-  size_t end;
+  const DependentString mStr;
+  String::size_type mPos;
+  String::size_type mEnd;
+  String::value_type mTerminator;
 public:
-  StringScanner(const std::u16string& str) : str(str), pos(0), end(str.length()) {}
+  explicit StringScanner(const String& str, String::size_type pos = 0,
+        String::value_type terminator = u'\0')
+      : mStr(str), mPos(pos), mEnd(str.length()), mTerminator(terminator) {}
 
-  bool done()
+  bool done() const
   {
-    return pos >= end;
+    return mPos >= mEnd;
   }
 
-  size_t position()
+  String::size_type position() const
   {
-    return pos - 1;
+    return mPos - 1;
   }
 
-  char16_t next()
+  String::value_type next()
   {
-    return done() ? u'\0' : str[pos++];
+    String::value_type result = done() ? mTerminator : mStr[mPos];
+    mPos++;
+    return result;
+  }
+
+  bool skipOne(String::value_type ch)
+  {
+    if (!done() && mStr[mPos] == ch)
+    {
+      mPos++;
+      return true;
+    }
+
+    return false;
+  }
+
+  bool skip(String::value_type ch)
+  {
+    bool skipped = false;
+    while ((skipped = skipOne(ch)));
+    return skipped;
   }
 };
-
-#endif