[Feature / Selectable A11y] making EuiSelectable[searchable] more accessible

[myasonik]

Summary

If EuiSelectable is also searchable it becomes an ARIA combobox. Largely, that means moving most of the aria-* props from the <ul> and onto the <input /> or surrounding <div>.

Largely this follows the 1.2 combobox spec with just a few fall back properties from 1.0 and 1.1.

Question!

Is this a breaking change?
EuiSelectableSearch and EuiSelectableList had prop changes but neither of those is really intended as a publicly consumable component individually though technically code be. The props for EuiSelectable have not changed.

Checklist

- [ ] Check against all themes for compatibility in both light and dark modes
- [ ] Checked in mobile
- [ ] Checked in IE11

• Checked in 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

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3234/

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3234/

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3234/

[thompsongl]

Is this a breaking change?

Yes. EuiSelectableList is part of the public API and now has 2 extra required props. Same with EuiSelectableSearch and its 1 new required prop. Whether they should be part of the public API is debatable, but removing them would also be a breaking change 😄

I noticed that the list in the 'Searchable' example no longer scrolls when operated with the keyboard. Is this intentional?

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3234/

[myasonik]

@thompsongl fixed!

[thompsongl]

Looking good 👍
Functionality remains unchanged

[thompsongl]

Just realized that this is going into a feature branch, so no CL entry is necessary.

LGTM; tested locally

[myasonik]

@cchaos did you still want to review this?

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3234/