fix: do not close popover on focusout after mousedown inside

[web-padawan]

Description

Part of #7652

Fixes the issue that happens on click inside the popover content when focus trigger is used. In this case, focusout event occurs and the overlay unexpectedly closes despite the fact that the click was inside the overlay.

The solution is to use mousedown event listener and set a flag to ignore next focusout event, if any.
The flag is then set back to false on mouseup using a global event listener.

Can be tested with the following HTML:

<button id="button">Open</button>
<vaadin-popover for="button"></vaadin-popover>

<script type="module">
  import '@vaadin/popover';

  const popover = document.querySelector('vaadin-popover');
  popover.trigger = ['focus'];

  popover.renderer = (root) => {
    if (!root.firstChild) {
      // root.appendChild(document.createElement('input'));
      const div = document.createElement('div');
      div.textContent = 'Some text content';
      root.appendChild(div)
    }
  };
</script>

Type of change

• Feature

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud