feat: remove Button translations and add inset shadow on active

[virajsanghvi]

Description

To avoid buttons physically moving, we've removed the translations on hover/focus and replaced it with an inset shadow (with existing removal of focus/active shadow). We will likely change/refine this behavior in the future, but this removes the weirdness of a physically moving button.

I changed the implementation of ouiSlightShadowActive because there were no active consumers in OUI or OpenSearch Dashboards.

The main downsides of this approach are when background is black and the button is white or a button icon without a border as these cases won't have a super visible change on active.

Item	Before (v7dark)	After (v7dark)	Before (v8dark)	After (v8dark)
Button
Empty Button (no change)
Button Icon
Toggle Button
Button Group (no change)
Ghost Button
Split Button

fyi: @lauralexis

Issues Resolved

N/A

Check List

• [ ] New functionality includes testing.
• [X] New functionality has been documented.
• [X] All tests pass
  • [X] yarn lint
  • [X] yarn test-unit
• [x] Update CHANGELOG.md
• [X] Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[ashwin-pc]

I'm good with removing the movement, but what's the reason for removing the shadow?

[virajsanghvi]

I'm good with removing the movement, but what's the reason for removing the shadow?

Adding the inset shadow on active had the effect of disabling the hover outer shadow. This is actually what some other design systems do - the inset basically makes the button looked depressed and the loss of the outer shadow in that state also helps in seeing something changed for colors that make the inset harder to see.

[ashwin-pc]

Oh my bad, I assumed that you removed it. That works. Thanks for the clarification