[a11y] Extend DemoController's alert auto-dismiss delay when vo is on

[joannaquu]

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

DemoController's showMessage has an auto dismiss option of 1 second. When voice over is running, this is too fast and ends up dismissing the alert before the alert message can be read. Update it to be 3 seconds when vo is on.

Verification

Before	After
https://github.com/user-attachments/assets/1edbf183-88e5-4ed9-a377-5e29244929dc	https://github.com/user-attachments/assets/cba02757-3d3d-4325-9a65-ebaafcc042a2

Pull request checklist

This PR has considered:

• Light and Dark appearances
• iOS supported versions (all major versions greater than or equal current target deployment version)
• VoiceOver and Keyboard Accessibility
• Internationalization and Right to Left layouts
• Different resolutions (1x, 2x, 3x)
• Size classes and window sizes (iPhone vs iPad, notched devices, multitasking, different window sizes, etc)
• iPad Pointer interaction
• SwiftUI consumption (validation or new demo scenarios needed)
• Objective-C exposure (provide it only if needed)

Microsoft Reviewers: Open in CodeFlow