Frame: Make TAS dialogs private

Amends the TAS callbacks to internally store functions using
std::function instead of raw function pointers. This allows binding
extra contextual state via lambda functions, as well as keeping the
dialogs internal to the main frame (on top of being a more flexible
interface).

Source/Core/DolphinWX/Debugger/CodeWindowFunctions.cpp

@@ -3,7 +3,9 @@
 // Refer to the license.txt file included.
 
 #include <cstddef>
+#include <fstream>
 #include <istream>
+#include <sstream>
 #include <string>
 #include <utility>
 #include <vector>