feat(react-switch): add disabledFocusable prop

[Copilot]

Switch lacked a disabledFocusable prop, forcing consumers to manually simulate visually-disabled-but-focusable behavior—leading to inconsistent, error-prone implementations. This adds disabledFocusable to Switch, consistent with Button and other Fluent UI interactive components.

Changes

• Switch.types.ts — Added disabledFocusable?: boolean to SwitchProps; added to SwitchState required picks
• useSwitch.tsx — When disabledFocusable=true:
  • Sets aria-disabled="true" on the <input> instead of disabled (keeps element in tab order)
  • Calls ev.preventDefault() in the change handler to block state mutation
  • Passes disabled || disabledFocusable to Label for consistent visual state
  • Excludes disabledFocusable from native props forwarded to <input>
• useSwitchStyles.styles.ts — Added [aria-disabled="true"] CSS selectors in useInputBaseClassName mirroring the :disabled rules. Key specificity considerations:
  • [aria-disabled="true"]:not(:checked) and [aria-disabled="true"]:checked variants match the specificity (0,4,0) of the :enabled:not(:checked) / :enabled:checked rules and are ordered after them in the reset class to win the cascade
  • Forced-colors variants (ButtonFace/GrayText) placed after :enabled:checked to override the Highlight active styles
• Switch.test.tsx — Added tests for focus retention, checked-state immutability, and onChange suppression when disabledFocusable
• SwitchDisabled.stories.tsx — Added unchecked and checked disabledFocusable examples

Usage

// Switch remains in the tab order and appears disabled, but focus is not lost
<Switch disabledFocusable label="Feature unavailable" />
<Switch checked disabledFocusable label="Active but locked" />

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