[BottomSheetController] Explicitly set isAccessibilityElement of resizingHandleView

[nodes11]

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

When the isExpandable state of the BottomSheetController changes to false, the resizingHandleView hides but its frame remains an accessible element in VoiceOver mode.

This change sets the isAccessibilityElement property when isExpandable changes.

Binary change

N/A

Verification

Validated in Fluent Demo Controller that the issue no longer reproduces.

Visual Verification

Before	After

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Simulator.Screen.Recording.-.iPhone.17.Pro.-.2025-10-27.at.10.04.50.mov

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Simulator.Screen.Recording.-.iPhone.17.Pro.-.2025-10-27.at.10.03.35.mov

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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)

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