[i18n] Support user defined component

[thompsongl]

Summary

Replaces #5236, which got into a bad git state (cc @ym)

We noticed that Chrome's built-in translation feature will break any page with EuiTable.

After investigation, I found that it's caused by the <Fragment> component used by EuiI18n and React or Chrome Trasnlate can't work together when we're using <Fragment> rather than a real DOM component here.

I see i18next has the option to use a different component and we can use the same approach in Eui to make a workaround. That's what the PR is for.

Reference:

[1] i18next/react-i18next#1254
[2] facebook/react#17256

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 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

[thompsongl]

FWIW I was going to approve the original PR after I added 489d981

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5337/

[cee-chen]

QA and basic functionality LGTM! I have some minor comments around the documentation/demo, but they're not blocking

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5337/