[EuiDataGrid] Enhance column header actions popover to be keyboard navigable with up/down arrow keys

[cee-chen]

Summary

EuiDataGrid changes

closes #4642

Look ma, no mouse!

Implementation should still respect native Tab behavior as it works off of document.activeElement.

EuiPopover changes

• I fixed a prop being incorrectly passed to the underlying DOM (4bff0b8)
• I added a popoverScreenReaderText prop to allow adding custom keyboard navigation instructions for SR users (689dd44):

Checklist

• Checked in Chrome, Safari, Edge, and Firefox
• Added or updated jest and cypress tests
• Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

- [ ] Checked in both light and dark modes
- [ ] Checked in mobile
- [ ] Props have proper autodocs and playground toggles
- [ ] Added documentation
- [ ] Checked Code Sandbox works for any docs examples
- [ ] Checked for breaking changes and labeled appropriately
- [ ] Updated the Figma library counterpart

[cee-chen]

Also wanted to mention - I did spike out converting EuiListGroup to an EuiContextMenuPanel, which comes with up/down arrow navigation OOTB, but unfortunately the way we've built the object configuration of our cell header actions is super specific to EuiListGroupItem props (see: column_actions.tsx). There's also a few props such as color which is unique to EuiListGroupItem that we wouldn't get for free from our context menus for example. That's not to say the conversion isn't possible, but I avoided it for now for the sake of not either introducing a breaking change or a lot of annoying-to-grok transmogging code. Also worth noting we would need to add a new xs size for EuiContextMenu, which is easy enough, but is something we would need to run by the designers to ensure it's OK for the component.

TL;DR I found it easier to write a bunch of index if statements lol 🤪

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_6017/

[1Copenut]

Really liking this enhancement. I left one copy suggestion / question, but have no items specifically to change. LGTM!

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_6017/

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_6017/

[chandlerprall]

LGTM; tested in the PR's published docs. ❤️ those tests