Keydown event frequency

Originally by @MTzukanov

Quote:
"The main problem is, that it's not possible to set a timout (or whatever) between several POST requests to the server-side.
So if a user holds down a shortcut key, e.g. ESC, each 2-3ms the server side will be informed with a POST request.

Example:

private final ShortcutListener escapseShortcutListener = new ShortcutListener("ESC key", KeyCode.ESCAPE, null)
{
    private static final long serialVersionUID = -8080266529606949440L;

    @Override
    public void handleAction(Object sender, Object target)
    {
        // sample code will be called here,
        // but should be not invoked for each 2-3ms
    }
};

So we need a new behavior to react on keyUp/keyDown events inside the shortcut listener.
As long as the button is hold down, only one event should be triggered.
Is this possible in Vaadin?

(Worstcase scenario: If ~ 400-1000 user use shortcuts in an excesive way, the impact on the server-side would be our bottleneck in future.)"

Imported from https://dev.vaadin.com/ issue #12374

Start by tracing ShortcutListener and its handleAction callback, then inspect how keydown and keyup events are sent to the server. Confirm the intended behavior from the issue: holding a shortcut should trigger only one event rather than repeated POST requests. No file or test is named in the payload, so the relevant entry point and validation coverage must first be located.