Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

Adds support for a new partial expansion state to bottom sheet. Most of the diff is fairly simple, the main behavioral change is that on pan end, we don't just determine the target state based on direction + velocity, but also position to see if we go towards .partial, .expanded, or .collapsed.

The other bigger change is the addition of the partialHeightResolver, which is needed to pull fresh height from the client. It follows design of the existing collapsedHeightResolver. I chose to cache them together, because we usually pull them together as well.

Some semantic choices had to be made, like isExpanded still maps to .expanded, which also means tapping the resizing handle while in .partial state takes the sheet to .expanded. That choice is fairly arbitrary, given that .partial is in-between by definition.

To enable the partial state, we don't have a distinct bool - it's just inferred from the existence of the partialHeightResolver.

Verification

Various manual testing in the demo app + sanity check with client team to early integrate and test E2E. Restricted height scenarios, landscape / portrait changes - verifying sheet frame recalculates to correct new calue.

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