[BottomSheetController] Update collapsedHeightInSafeArea for partial expansion state

[nodes11]

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

The collapsedHeightInSafeArea is always set using the sheet’s .collapsed state offset, which doesn't support sheets that open to the .partial state. This can cause UI that should show above the sheet to get hidden behind the sheet because safe area does not get updated correctly.

To fix this, if the targetExpansionState is .partial, calculate the offset using .partial, otherwise use .collapsed.

Binary change

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

Verification

Validated that internal use cases are resolved with this change.

Visual Verification

Before	After
Screenshot or description before this change	Screenshot or description with this change

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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