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/fold.c b/src/fold.c
index 229cb2a..f94b389 100644
--- a/src/fold.c
+++ b/src/fold.c
@@ -1499,7 +1499,7 @@
 	line2 = line1 - amount_after - 1;
     // If appending a line in Insert mode, it should be included in the fold
     // just above the line.
-    if ((State & INSERT) && amount == (linenr_T)1 && line2 == MAXLNUM)
+    if ((State & MODE_INSERT) && amount == (linenr_T)1 && line2 == MAXLNUM)
 	--line1;
     foldMarkAdjustRecurse(&wp->w_folds, line1, line2, amount, amount_after);
 }
@@ -1523,7 +1523,7 @@
 
     // In Insert mode an inserted line at the top of a fold is considered part
     // of the fold, otherwise it isn't.
-    if ((State & INSERT) && amount == (linenr_T)1 && line2 == MAXLNUM)
+    if ((State & MODE_INSERT) && amount == (linenr_T)1 && line2 == MAXLNUM)
 	top = line1 + 1;
     else
 	top = line1;