[client,SDL] add CStringPtr type

Allows wrapping allocated C strings to automatically free them when no
longer used.

client/SDL/common/sdl_common_utils.hpp

@@ -19,8 +19,12 @@
  */
 #pragma once
 
+#include <memory>
+
 #include <freerdp/settings_types.h>
 
+using CStringPtr = std::unique_ptr<char, decltype(std::free)*>;
+
 bool operator==(const MONITOR_ATTRIBUTES& l, const MONITOR_ATTRIBUTES& r);
 bool operator==(const rdpMonitor& l, const rdpMonitor& r);