Introduce function for directly updating GDB's screen dimensions

... to replace the roundabout pattern of

  execute_command ("set width %d");
  execute_command ("set height %d");

for doing the same thing.

gdb/ChangeLog:

	* utils.h (set_screen_width_and_height): Declare.
	* utils.c (set_screen_width_and_height): Define.
	* tui/tui-win.c (tui_update_gdb_sizes): Use it.

gdb/utils.c

@@ -1795,6 +1795,18 @@ set_height_command (char *args, int from_tty, struct cmd_list_element *c)
   set_screen_size ();
 }
 
+/* See utils.h.  */
+
+void
+set_screen_width_and_height (int width, int height)
+{
+  lines_per_page = height;
+  chars_per_line = width;
+
+  set_screen_size ();
+  set_width ();
+}
+
 /* Wait, so the user can read what's on the screen.  Prompt the user
    to continue by pressing RETURN.  */