use of C++ API for running a file (bug #42307) * octave-cmd.cc: New file providing the new command class octave_cmd; (prepare_command_editor): common action that all derived command classes use for method execute; (octave_cmd_exec::execute): execute method of derived class for executing ordinary commands in the terminal; (octave_cmd_eval::execute): execute method of derived class for running a file (as function if it is a valid identifier or as script) * octave-cmd.h: providing base and derived classes * main-window.cc (main_window): _cmd_queue is not a pointer anymore; (~main_window): _cmd_queue is not a pointer anymore; (execute_command_in_terminal): use new command class for queuing a command; (run_file_in_terminal): check for valid identifier moved from here to the execute method of the related command class; (run_file_callback): use new class for queuing command, path check moved from here into the execute method of the command class; (queue_command): gets new command class instead of a string as input; (closeEvent): queue command class instead of string; (execute_command_callback): command queue contains command class instances; * main-window.h: use new octave-cmd class for queue_command, the command queue is not a pointer anymore * module.mk: new files octave-cmd.cc and octave-cmd.h