[EuiComboBox] autoFocus behavior

[thompsongl]

Summary

Adds a top-level autoFocus prop that gets passed through to the input, enabling native HTML autofocus behavior.

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 the 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

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_4772/

[cchaos]

LGTM. Tested the temporary example (in Chrome only). Have you also tested this behavior in portal content like popover or flyout?

[thompsongl]

Have you also tested this behavior in portal content like popover or flyout?

I haven't but I will. Popovers, portals, etc. have their own initial focus methods that are more heavy-handed and will likely take precedence.

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_4772/

[thompsongl]

Popovers, portals, etc. have their own initial focus methods that are more heavy-handed and will likely take precedence.

I was incorrect. autoFocus works in modals and flyouts, and takes precedence over those initial focus methods. This is true for any component or DOM element that supports autoFocus (basically all EUI form controls, now including EuiComboBox).

[cchaos]

I think that makes the most sense?

[thompsongl]

I think that makes the most sense?

I agree. Use/mimic the native browser API as much as possible.