Add accessibilityValue support to Button component

[Copilot]

Summary

This PR implements support for accessibilityValue prop in the React Native Windows Button component, enabling proper propagation of accessibility values from JavaScript to the native C++ layer.

Problem

The Button component in Button.windows.js was missing support for the accessibilityValue prop and related aria-value* props, which prevented accessibility values from being passed through to the underlying TouchableHighlight component. This was identified in the existing ButtonExample where accessibilityValue={{Text: 'Submit Application'}} was being used but not actually supported by the component.

Changes Made

1. Type Support

• Added AccessibilityValue import from ./View/ViewAccessibility
• Added accessibilityValue?: ?AccessibilityValue to ButtonProps type definition
• Added aria-valuemax, aria-valuemin, aria-valuenow, and aria-valuetext props with proper typing

2. Component Logic

• Added extraction of accessibilityValue and aria-value* props in component destructuring
• Implemented _accessibilityValue computation logic that mirrors the View component implementation
• Added proper fallback logic where aria-value* props take precedence over accessibilityValue object properties

3. Prop Propagation

• Added accessibilityValue={_accessibilityValue} to TouchableHighlight in both Windows and non-Windows code paths
• Ensures accessibility values are properly passed to the native layer

4. Example Updates

• Fixed existing ButtonExample.windows.js to use correct property case (text instead of Text)
• Added demonstration of aria-value* props usage alongside accessibilityValue

Usage Examples

After this change, Button components now support both forms of accessibility value specification:

// Using accessibilityValue object
<Button
  title="Progress Button"
  accessibilityValue={{
    min: 0,
    max: 100,
    now: 75,
    text: "75 percent complete"
  }}
/>

// Using individual aria-value* props
<Button
  title="Progress Button"
  aria-valuemin={0}
  aria-valuemax={100}
  aria-valuenow={75}
  aria-valuetext="75 percent complete"
/>

Testing

• Verified syntax with Node.js parser
• Confirmed type imports are correct and consistent with View component
• Updated existing ButtonExample to demonstrate the functionality
• Implementation follows exact same pattern as View.windows.js for consistency

Fixes #14902.

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