Replaced root element of EuiFlyout

[andreadelrio]

Summary

Replaced span with Fragment as the root element of EuiFlyout. Fixes #1488

Checklist

- [ ] Checked in dark mode
- [ ] Checked in mobile
- [ ] Checked in IE11 and Firefox
- [ ] Props have proper autodocs
- [ ] Added documentation 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

[thompsongl]

LGTM!
Tested locally and all interactions remain as they were

[cchaos]

@thompsongl You mentioned in the issue that using Fragment caused issues in certain cases. #1488 (comment)

Is that still the case?

[thompsongl]

@cchaos Nope. At the time of that comment, EUI was still using the old focus trap/lock library. Since updating, the root of the problem is not applicable.

I should've noted that @andreadelrio and I had an Slack conversation about this before she started work here. Thanks for bringing it up here.

[cchaos]

Cool! Then 👍