patch 8.2.3969: value of MAXCOL not available in Vim script

Problem:    Value of MAXCOL not available in Vim script.
Solution:   Add v:maxcol. (Naohiro Ono, closes #9451)
diff --git a/src/vim.h b/src/vim.h
index 21832ab..87fdbb1 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -2067,7 +2067,8 @@
 #define VV_SIZEOFINT	100
 #define VV_SIZEOFLONG	101
 #define VV_SIZEOFPOINTER 102
-#define VV_LEN		103	// number of v: vars
+#define VV_MAXCOL	103
+#define VV_LEN		104	// number of v: vars
 
 // used for v_number in VAR_BOOL and VAR_SPECIAL
 #define VVAL_FALSE	0L	// VAR_BOOL