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/gui_gtk.c b/src/gui_gtk.c
index 0b98fd4..1ae15ca 100644
--- a/src/gui_gtk.c
+++ b/src/gui_gtk.c
@@ -691,7 +691,7 @@
     char_u	*tooltip;
     static int	did_msg = FALSE;
 
-    if (State & CMDLINE)
+    if (State & MODE_CMDLINE)
 	return;
     menu = (vimmenu_T *)data;
     tooltip = CONVERT_TO_UTF8(menu->strings[MENU_INDEX_TIP]);