fix(api): update grid cursor in nvim_win_set_cursor()

Problem:  Cursor position set by nvim_win_set_cursor() is not reflected
          on the screen when followed by a blocking call like getchar().
Solution: Immediately update the cursor position on the grid.

src/nvim/api/window.c

@@ -148,7 +148,7 @@ void nvim_win_set_cursor(Window window, ArrayOf(Integer, 2) pos, Error *err)
   switchwin_T switchwin;
   switch_win(&switchwin, win, NULL, true);
   update_topline(curwin);
-  validate_cursor(curwin);
+  setcursor_mayforce(true);
   restore_win(&switchwin, true);
 
   redraw_later(win, UPD_VALID);