Properly render an example's html output in the Demo HTML tab

[chandlerprall]

Summary

Fixes #2713 and fixes #2711

Two issues I found:

• Any example source that returns a <Fragment> (e.g. list_group.js only rendered the first child's html
• The rendered content didn't include the root node's HTML, so every Demo HTML tab in our docs has been missing it's top-most wrapping element.

Both of these are fixed by wrapping the rendered source component in a div.

@thompsongl for code review
@snide / @cchaos to double check the Demo HTML output

Checklist

- [ ] Check against all themes for compatability in both light and dark modes
- [ ] 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]

Code changes and output both look good

[cchaos]

👍 Fixes those issues and I didn't see any regressions of existing examples. Perhaps unrelated, but none of the DataGrid examples display the HTML.

[chandlerprall]

Will look into the datagrid's lack of HTML separately. Took a peek, looks like a different issue.