(Accessibility) Fix EuiNavDrawerFlyout using <h5> by replacing with <div>

[PhilippBaranovskiy]

Fixes #2039
Associated issue: elastic/kibana#34995

Summary

This PR replaces <h5> with <div> and that's it.

Checklist

• This was checked in mobile
• This was checked in IE11
• This was checked in dark mode
• Any props added have proper autodocs
• Documentation examples were added
• A changelog entry exists and is marked appropriately
• This was checked for breaking changes and labeled appropriately
• Jest tests were updated or added to match the most common scenarios
• This was checked against keyboard-only and screenreader scenarios
• This required updates to Framer X components

[PhilippBaranovskiy]

jenkins, test this

[ryankeairns]

Checked this out locally and it looks good.

It does make me wonder if we're offering a subpar experience for screenreader users given our lack of proper headings, generally speaking. Then again, we don't have control of content and each app is quite different, so I don't see how we could keep that organized enough to be accessible and useful.

One other thought, @snide should we be labeling the EuiNavDrawer as a main navigation region in Kibana?

[cchaos]

I agree with @ryankeairns that more thought should be put into the full accessibility (screen-reader) experience of the nav drawer in association with the application it sits within.