DolphinQt: Handle non-ASCII characters in Windows cmd arguments

CommandLineParse expects UTF-8 strings. (QApplication, on the
other hand, seems to be designed so that you can pass in the
char** argv untouched on Windows and get proper Unicode handling.)

Source/Core/Common/StringUtil.h

@@ -236,3 +236,7 @@ inline bool IsPrintableCharacter(char c)
 {
   return std::isprint(c, std::locale::classic());
 }
+
+#ifdef _WIN32
+std::vector<std::string> CommandLineToUtf8Argv(const wchar_t* command_line);
+#endif