### Problem Description
I use ubuntu linux. my system language is Chinese, but the dialog button labels is English by default. I found the buttonLabel option from the API to set the label of the save or open button, but the label of the cancel button is not supported.

### Proposed Solution
Support customizing cancel button label in Open and Save dialogs

shell/browser/ui/file_dialog_gtk.cc
gchar* filename =
      gtk_file_chooser_get_preview_filename(GTK_FILE_CHOOSER(chooser));
  if (!filename) {
    gtk_file_chooser_set_preview_widget_active(GTK_FILE_CHOOSER(chooser),
                                               FALSE);
    return;
  }
  
  
  struct stat stat_buf;
  if (stat(filename, &stat_buf) != 0 || !S_ISREG(stat_buf.st_mode)) {
    g_free(filename);
    gtk_file_chooser_set_preview_widget_active(GTK_FILE_CHOOSER(chooser),
                                               FALSE);
    return;
  }
  
  GdkPixbuf* pixbuf = gdk_pixbuf_new_from_file_at_size(filename, kPreviewWidth,
                                                       kPreviewHeight, nullptr);
  g_free(filename);
  if (pixbuf) {
    gtk_image_set_from_pixbuf(GTK_IMAGE(preview_), pixbuf);
    g_object_unref(pixbuf);
  }
  gtk_file_chooser_set_preview_widget_active(GTK_FILE_CHOOSER(chooser),
                                             pixbuf ? TRUE : FALSE);
}
}  
bool ShowOpenDialogSync(const DialogSettings& settings,