fix conflict between main and editor menus when using alt keys (bug #42659) * file-editor.cc (enable_menu_shortcuts): new function enabling/disabling the alt-key accelerators; (m_add_menu): new function adding a menu and storing menu title with and without the char & indicating the accelerator in a hash; (construct): use m_add_menu for adding a new menu to the menu bar * file-editor-interface.h: new virtual function enable_menu_shortcuts * file-editor.h: new functions enable_menu_shortcuts amd m_add_menu, new hash for storing the menu titles * main-window.cc (connect_visibility_changed): disable editors menu shortcuts; (enable_menu_shortcuts): new function enabling/disabling the alt-key accelerators; (m_add_menu): new function adding a menu and storing menu title with and without the char & indicating the accelerator in a hash; (construct_file_menu, construct_edit_menu, construct_debug_menu, construct_window_menu, construct_help_menu, construct_news_menu): use m_add_menu for adding a new menu to the menu bar; (set_global_edit_shortcuts): enable/disable the main and the editors menu shortcuts