[Bottom Sheet] Add prioritizesSheetPanWhenCollapsed property

[lukas-cap]

When enabled, the sheet's pan gesture takes priority over all content gestures while collapsed. Content gestures are deferred until the sheet pan fails (e.g. horizontal swipe or tap). This enables scroll blocking for SwiftUI content where hostedScrollView cannot be provided.

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

(a summary of the changes made, often organized by file)

Binary change

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

Verification

(how the change was tested, including both manual and automated tests)

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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