patch 8.2.4744: a terminal window can't use the bell

Problem:    A terminal window can't use the bell.
Solution:   Add bell support for the terminal window. (closes #10178)
diff --git a/src/terminal.c b/src/terminal.c
index b6efb49..9f9e84a 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -3385,12 +3385,22 @@
     limit_scrollback(term, &term->tl_scrollback, TRUE);
 }
 
+/*
+ * Called when the terminal wants to ring the system bell.
+ */
+    static int
+handle_bell(void *user UNUSED)
+{
+    vim_beep(BO_SH);
+    return 0;
+}
+
 static VTermScreenCallbacks screen_callbacks = {
   handle_damage,	// damage
   handle_moverect,	// moverect
   handle_movecursor,	// movecursor
   handle_settermprop,	// settermprop
-  NULL,			// bell
+  handle_bell,		// bell
   handle_resize,	// resize
   handle_pushline,	// sb_pushline
   NULL			// sb_popline