EuiNavDrawer a11y, pt. 1

[thompsongl]

Summary

Chipping away at #2252

• On clicking the expand/collapse button, focus management is lost and is returned to the body. (It should stay on the button.)

• The dock/undock button should have aria-pressed=true|false defined to communicate state. This can replace the role=switch and aria-checked=true|false

• Some clean up to remove an unused method and an outdated comment

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

[myasonik]

LGTM!

[snide]

Needs a CL, otherwise looks good.