[confirm-dialog] Confirm dialog closes on holding space

[yuriy-fix]

Description of the bug (can be considered as edge case)

confirm-dialog is moving the focus to the confirmButton when opens. So in case it set to be opened on keydown, if you press and hold space for some time (it will start dispatching huge amount of keydown events), the dialog will be opened and on release (keyup is dispatched and click afterwards) the confirmButton will be clicked, so it will be closed right away.

Minimal reproducible example

<vaadin-button>Open dialog</vaadin-button>
<vaadin-confirm-dialog header="Meeting starting" confirm-text="OK">
  Your next meeting starts in 5 minutes
</vaadin-confirm-dialog>

const dialog = document.querySelector('vaadin-confirm-dialog');
const button = document.querySelector('vaadin-button');

button.addEventListener('keydown', function(event) {
  if (/^( |SpaceBar)$/.test(event.key)) {
    dialog.opened = true;
  }
});

1. Use the code (modified demo example)
2. Focus the Open dialog button, i.e. with Tab
3. Hold Space
4. Release once dialog is opened.

Expected behaviour

Dialog remains opened

Actual behavior:

Dialog is auto-closed