patch 8.2.2324: not easy to get mark en cursor posotion by character count

Problem:    Not easy to get mark en cursor posotion by character count.
Solution:   Add functions that use character index. (Yegappan Lakshmanan,
            closes #7648)
diff --git a/src/typval.c b/src/typval.c
index 06276b4..7e4e63d 100644
--- a/src/typval.c
+++ b/src/typval.c
@@ -1579,7 +1579,7 @@
     if (lnum <= 0)  // no valid number, try using arg like line()
     {
 	int	fnum;
-	pos_T	*fp = var2fpos(&argvars[0], TRUE, &fnum);
+	pos_T	*fp = var2fpos(&argvars[0], TRUE, &fnum, FALSE);
 
 	if (fp != NULL)
 	    lnum = fp->lnum;