[EuiDataGrid] Remove cell actions onmouseleave

[chandlerprall]

Summary

Fixes #5116

Datagrid cells avoid rendering their cell actions unless the cell is focused or the mouse cursor is over the cell. To handle the mouse hovering interaction, we set an internal state on the cell but never unset it when the mouse leaves, which left all the action DOM in place even when it's hidden. This PR resets that state onMouseLeave, removing the cell action buttons from the DOM when not needed.

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_5120/

[cchaos]

Is it also possible to prevent the reanimation of the expand button when the cell is in focus?

[cee-chen]

Not sure if we want to block this PR to figure out the animation issue Caroline highlighted, but code-wise at least this LGTM. Depending on whether this or #5125 gets in first, I can add a small .simulate unit test as well for this event.

[chandlerprall]

Is it also possible to prevent the reanimation of the expand button when the cell is in focus?

I wasn't able to find an obvious quick fix, I'll see if there's not already an issue for that and if not, make one.

EDIT now tracked in #5134

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5120/