Add a simple FileSystemPath class that can canonicalize paths.

Also a simple StringBuilder to help him out.

AK/FileSystemPath.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include "String.h"
+
+namespace AK {
+
+class FileSystemPath {
+public:
+    FileSystemPath() { }
+    explicit FileSystemPath(const String&);
+
+    bool isValid() const { return m_isValid; }
+    String string() const { return m_string; }
+
+private:
+    bool canonicalize(bool resolveSymbolicLinks = false);
+
+    String m_string;
+    bool m_isValid { false };
+};
+
+};
+
+using AK::FileSystemPath;