Request xterm 'modifyOtherKeys' mode to opt-in CSI u key reporting

Various terminal emulators now support this `CSI > 4 ; 1 m` sequence
to enable CSI u style reporting, opt into it on startup.

Closes #4103

src/ncurses_ui.cc

@@ -412,6 +412,8 @@ void NCursesUI::set_terminal_mode() const
     fputs("\033=", stdout);
     // force enable report focus events
     fputs("\033[?1004h", stdout);
+    // request CSI u style key reporting
+    fputs("\033[>4;1m", stdout);
     fflush(stdout);
 }
 
@@ -420,6 +422,7 @@ void NCursesUI::restore_terminal_mode() const
     tcsetattr(STDIN_FILENO, TCSAFLUSH, &m_original_termios);
     fputs("\033>", stdout);
     fputs("\033[?1004l", stdout);
+    fputs("\033[>4;0m", stdout);
     fflush(stdout);
 }