Add expanded/collapsed state support for SwiftUI DisclosureGroup

[RoyalPineapple]

Summary

Adds support for reading the expanded/collapsed state from SwiftUI DisclosureGroup and expandable list sections, so accessibility snapshots now show whether these elements are expanded or collapsed — matching what VoiceOver announces to users.

What changed

• New ExpandedStatus enum on AccessibilityElement — unsupported, expanded, collapsed
• Reads _accessibilityExpandedStatus via the ObjC runtime on each accessibility element during parsing
• Appends status to VoiceOver description — e.g. "Section. Button. Heading. Expanded."
• Appends hint — "Double tap to collapse." / "Double tap to expand.", appended to any existing hint
• Localized strings for en, de, ru
• Demo view + snapshot test for DisclosureGroup with reference images on iOS 17.5, 18.5, 26.2

Why the private API

The public iOS 18 accessibilityExpandedStatus property exists but does not work on SwiftUI nodes — SwiftUI's AccessibilityNode overrides only the private _accessibilityExpandedStatus method. We verified this thoroughly through runtime introspection:

Finding	Detail
Both APIs declared on NSObject	_accessibilityExpandedStatus (getter) and accessibilityExpandedStatus (getter/setter) are both declared directly on NSObject
Public setter syncs to private getter	On stock UIView/NSObject, setting the public property always updates the private getter — they share backing storage
No private setter exists	_setAccessibilityExpandedStatus: does not exist on any class; the private key is also not KVC-compliant
Subclass override is the only way they diverge	SwiftUI.AccessibilityNode overrides _accessibilityExpandedStatus to read from SwiftUI's internal accessibility graph, bypassing the shared storage entirely
VoiceOver reads the private getter	When public and private values conflict, VoiceOver announces what _accessibilityExpandedStatus returns — confirmed on-device with iPhone 15
Rapid toggling never desyncs	On stock views, pub/priv stay perfectly in sync across all permutations

Conclusion: Reading _accessibilityExpandedStatus is correct because it is the single source of truth that both SwiftUI (via subclass override) and UIKit (via the public setter's internal sync) funnel into. The public API is actually less reliable — it misses all SwiftUI elements entirely.

We use responds(to:) + method(for:) to read the value, consistent with how the codebase already reads other private accessibility properties.

Data flow

flowchart LR
    A["SwiftUI DisclosureGroup"] -->|"_accessibilityExpandedStatus"| B["NSObject extension\n(runtime read)"]
    B -->|"ExpandedStatus enum"| C["AccessibilityElement\n.expandedStatus"]
    B -->|"rawStatus 1/2"| D["Description: 'Expanded.' / 'Collapsed.'"]
    B -->|"rawStatus 1/2"| E["Hint: 'Double tap to collapse/expand.'"]
    D --> F["Snapshot Legend"]
    E --> F

Loading

Snapshot output

Before:

Section Header. Button. Heading.
  Hint: (none)

After:

Section Header. Button. Heading. Expanded.
  Hint: Double tap to collapse.

Test plan

• SwiftUIDisclosureGroupTests snapshot test passes on iOS 17.5, 18.5, 26.2
• All existing snapshot tests unaffected
• Build succeeds after rebase onto main
• Runtime sync investigation: 12/12 tests pass confirming private API behavior
• On-device VoiceOver verification with iPhone 15