patch 8.2.4911: the mode #defines are not clearly named

Problem:    The mode #defines are not clearly named.
Solution:   Prepend MODE_.  Renumber them to put the mapped modes first.
diff --git a/src/insexpand.c b/src/insexpand.c
index 2c549f8..86c6a14 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -2883,7 +2883,7 @@
 		|| check_for_list_arg(argvars, 1) == FAIL))
 	return;
 
-    if ((State & INSERT) == 0)
+    if ((State & MODE_INSERT) == 0)
     {
 	emsg(_(e_complete_can_only_be_used_in_insert_mode));
 	return;