@PreserveOnRefresh does not retain button click shortcuts

[alejandro-du]

Description of the bug

@PreserveOnRefresh doesn't retain button click shortcuts after browser refresh.

Minimal reproducible example

@Route
@PreserveOnRefresh
public class MainView extends Div {

    public MainView() {
        Button button = new Button("Press ENTER, reload the page, and press ENTER again",
                event -> Notification.show("Thanks"));
        button.addClickShortcut(Key.ENTER);
        add(button);
    }

}

Expected behavior

Click shortcuts work after a browser refresh.

Actual behavior

Click shortcuts don't work after a browser refresh.

Versions:

- Vaadin / Flow version: Vaadin 14.1.27
- Java version: openjdk 11.0.6 2020-01-14
- OS version: MacOS 10.15.4
- Browser version (if applicable):
- Application Server (if applicable):
- IDE (if applicable):

See also #6357.

[denis-anisimov]

Confirmed.
Thank you very much for the short and exact steps to reproduce.