[EuiSelectable] Fix logic to detect the blur event coming from child popover

[afharo]

Summary

Resolves #5020 (and probably #4147).

The current logic to detect if EuiSelectable was losing focus due to its popover was not working. Probably because the HTMLElement didn't actually contain the popover.

This PR changes the logic to check the popover's List ID to match the assigned rootId in the EuiSelectable.

Checklist

• Check against all themes for compatibility in both light and dark modes
• Checked in mobile
• Checked in Chrome, Safari, Edge, and Firefox
  - [ ] Props have proper autodocs and playground toggles
  - [ ] Added documentation
• Checked Code Sandbox works for the any docs examples
• Added or updated jest tests
• Checked for breaking changes and labeled appropriately
• Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5021/

[myasonik]

🤔 It's hard to do any keyboard or screen reader usage as, apparently, this has become totally broken at some point and using arrow keys and enter to use this component doesn't work at all.

The code change looks fine (the bug is in master so it's definitely not related) but it makes me uncertain on how to really test this thoroughly...

[cchaos]

Weird, I just checked out published docs, and I have no trouble using the keyboard to navigate.

Screen.Recording.2021-08-12.at.11.50.52.AM.mp4

[myasonik]

Ugh, ignore me. This is an old problem of mine that I keep forgetting about - has bit me several times.

For whatever reason, my external keyboard (and no one else's) does this. As soon as I use any other keyboard it's all fine.

---

Code looks good; Tested in FF and Edge. Can be approved after checklist is completed.

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5021/

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5021/

[cchaos]

Functionally tests right to me. @chandlerprall can you double-check the code?

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5021/

[thompsongl]

it looks like the issue has been there since 7.12.0. So, if we could backport it to 7.14.1 with a low risk upgrade, it’d be great
― @afharo

Just noting that that we should look at backporting this once it merges

[chandlerprall]

Change LGTM; Tested via the test deployment

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5021/