### 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
for (size_t i = 0; i < filters.size(); ++i) {
    const Filter& filter = filters[i];
    GtkFileFilter* gtk_filter = gtk_file_filter_new();
    for (size_t j = 0; j < filter.second.size(); ++j) {
      auto file_extension =
          std::make_unique<std::string>("." + filter.second[j]);
      gtk_file_filter_add_custom(
          gtk_filter, GTK_FILE_FILTER_FILENAME,
          reinterpret_cast<GtkFileFilterFunc>(FileFilterCaseInsensitive),
          file_extension.release(),
          reinterpret_cast<GDestroyNotify>(OnFileFilterDataDestroyed));
    }
    gtk_file_filter_set_name(gtk_filter, filter.first.c_str());
    gtk_file_chooser_add_filter(GTK_FILE_CHOOSER(dialog_), gtk_filter);
  }
}
void FileChooserDialog::OnUpdatePreview(GtkWidget* chooser) {