[EuiButton] Use euiDisabledSelector in useEuiButtonColorCSS

[mgadewoll]

Summary

This PR is a tiny follow-up to #9201 which introduced custom disabled behavior for buttons via aria-disabled. To support the change in styles, we added the helper selector euiDisabledSelector that combines :disabled and [aria-disabled="true"] selectors.

This PR updates the shared button styles in useEuiButtonColorCSS to use the new euiDisabledSelector. This update is mainly a cleanup/enhancement as the styles were also working as expected before for EUI button components as pointer events are removed.

Why are we making this change?

💪 Robustness: Ensures that potential custom usages of useEuiButtonColorCSS would correctly handle custom disabled selectors via aria-disabled too.

Impact to users

🟢 There are no changes required on consumer side.

QA

🧪 Storybook:

• EuiButton
• EuiButtonEmpty
• EuiButtonIcon
• EuiButtonGroup
• EuiFilterButton

Checks:

• verify hover states work as expected for EUI button components (with hasDisabled set to true or false as well as isDisabled set to true or false) and that there is no regression with production

General checklist

• Browser QA
  • Checked in both light and dark modes
  • Checked in both MacOS and Windows high contrast modes
    • (emulate forced colors if you do not have access to a Windows machine.)
  • Checked in mobile
  • Checked in Chrome, Safari, Edge, and Firefox
  • Checked for accessibility including keyboard-only and screenreader modes
• Docs site QA
  • Added documentation
  • Props have proper autodocs (using @default if default values are missing) and playground toggles
  • Checked Code Sandbox works for any docs examples
• Code quality checklist
  • Added or updated jest and cypress tests
  • Updated visual regression tests
• Release checklist
  • A changelog entry exists and is marked appropriately
  • If applicable, added the breaking change issue label (and filled out the breaking change checklist)
  • If the changes unblock an issue in a different repo, smoke tested carefully (see Testing EUI features in Kibana ahead of time)
• Designer checklist
  • If applicable, file an issue to update EUI's Figma library with any corresponding UI changes. (This is an internal repo, if you are external to Elastic, ask a maintainer to submit this request)

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 1f5a113
• Documentation website
• Storybook

cc @mgadewoll

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 1f5a113

cc @mgadewoll