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.

src/tag.c

@@ -2642,7 +2642,7 @@ findtags_add_match(
 		vim_strncpy(mfp, tagpp->tagname, len);
 
 	    // if wanted, re-read line to get long form too
-	    if (State & INSERT)
+	    if (State & MODE_INSERT)
 		st->get_searchpat = p_sft;
 	}
     }