[fluentui-apple] Have resizingHandleView overlap content in BottomSheetController

[veronicasalas]

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

In iOS 26, the bottom sheet’s content is designed to align concentrically with the sheet’s rounded corners. However, the presence of the resizingHandleView introduces a visible gap between the content and the corner, breaking this concentric alignment.

To address this, the resizingHandleView needs to overlap the bottom sheet’s content, so I’m introducing the new property, shouldResizingViewOverlayContent, which enables this behavior when set to true (the default is false). Additionally, the resizingHandleView is moved to become a subview of bottomSheetContentView

When this option is enabled, the constant between the resizingHandleView bottomAnchor and the stackView topAnchor is the resizing handle height so that the resizing handle overlays the content.

Binary change

(how is our binary size impacted -- see https://github.com/microsoft/fluentui-apple/wiki/Size-Comparison)

Verification

Visual Verification

bottom_sheet_controller_screenrecording.mov

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

[joannaquu]

nit: update view hierarchy on line 470