patch 8.2.3864: cannot disable requesting key codes from xterm

Problem:    Cannot disable requesting key codes from xterm.
Solution:   Add the 'xtermcodes' option, default on.
diff --git a/src/optiondefs.h b/src/optiondefs.h
index c392442..cc4ad9e 100644
--- a/src/optiondefs.h
+++ b/src/optiondefs.h
@@ -2941,6 +2941,9 @@
     {"writedelay",  "wd",   P_NUM|P_VI_DEF,
 			    (char_u *)&p_wd, PV_NONE,
 			    {(char_u *)0L, (char_u *)0L} SCTX_INIT},
+    {"xtermcodes",  NULL,   P_BOOL|P_VI_DEF,
+			    (char_u *)&p_xtermcodes, PV_NONE,
+			    {(char_u *)TRUE, (char_u *)0L} SCTX_INIT},
 
 // terminal output codes
 #define p_term(sss, vvv)   {sss, NULL, P_STRING|P_VI_DEF|P_RALL|P_SECURE, \