Button: replace :has([data-kbd-chord]) with a data attribute set from React #8724

Part of #8676 (P3).

Problem

Button/ButtonBase.module.css:28 and :217 use &:has([data-kbd-chord]), which applies to every Button. A :has() selector makes the browser re-check the button whenever its descendants change. Earlier work (#8115, #7901) removed many similar :has() selectors.

Proposed fix

Set a data-* attribute on the button from React when it renders a keybinding hint, as ActionList does for its item state. Then select on that attribute instead of :has().

Acceptance criteria

• ButtonBase.module.css no longer uses :has([data-kbd-chord]).
• Buttons with and without a keybinding hint look the same as before. Check the VRT snapshots for the affected stories.