patch 8.2.0774: t_TI and t_TE are output when using 'visualbell'

Problem:    t_TI and t_TE are output when using 'visualbell'. (Dominique
            Pelle)
Solution:   Do not change the terminal mode for a short sleep.  Do not output
            t_TI and t_TE when switching to/from TMODE_SLEEP. Make tmode an
            enum.
diff --git a/src/os_win32.c b/src/os_win32.c
index d77e216..edd5cda 100644
--- a/src/os_win32.c
+++ b/src/os_win32.c
@@ -3600,7 +3600,7 @@
  * set the tty in (raw) ? "raw" : "cooked" mode
  */
     void
-mch_settmode(int tmode)
+mch_settmode(tmode_T tmode)
 {
     DWORD cmodein;
     DWORD cmodeout;