fix(a11y): add List and ListItem accessibility roles & collection met…

[Ajeethundal]

Summary:

Resolves #30973, #30974, #30975, and #30977.

Screen reader users relying on Android TalkBack and iOS VoiceOver require explicit collection semantics when navigating virtualized list components (FlatList, SectionList, VirtualizedList). Without these, screen readers treat items as isolated, uncounted views instead of announcing:

• "In list, N items" when focusing the list container.
• "Item X of Y" when focusing an item.
• "Showing items X to Y of Z" when scrolling through list items.

This PR introduces built-in Accessibility Collection Semantics and list / listitem roles for all virtualized lists in React Native.

Key Implementation Highlights:

1. View Accessibility Interface (ViewAccessibility.js):

   • Added 'listitem' to AccessibilityRole.
   • Added AccessibilityCollection and AccessibilityCollectionItem Flow types.
   • Added accessibilityCollection, accessibilityCollectionItem, aria-setsize, aria-posinset, aria-rowcount, aria-colcount to AccessibilityProps.

2. Item-Level Semantics (VirtualizedListCellRenderer.js):

   • Automatically attaches accessibilityRole="listitem", aria-setsize={totalCount}, aria-posinset={index + 1}, and accessibilityCollectionItem (calculating dynamic rowIndex and columnIndex).

3. Container-Level Semantics (VirtualizedList.js):

   • Outer list container automatically receives accessibilityRole="list" (or "grid" when numColumns > 1), aria-rowcount, and accessibilityCollection.

4. Multi-Column Grid & Edge-Case Protections:

   • Grid Support (numColumns > 1): Dynamically computes row indices and column indices for multi-column FlatList grid layouts.
   • Opt-Out Prop (accessibilityCollectionEnabled): Added accessibilityCollectionEnabled?: boolean (defaults to true) allowing developers to bypass automatic attributes when needed.
   • Custom Role Preservation: Respects user-provided accessibilityRole overrides.

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Changelog:

[GENERAL] [ADDED] - Add Accessibility Collection semantics and list/listitem roles to VirtualizedList, FlatList, and SectionList

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Test Plan:

Automated Tests

• Ran unit test suite in VirtualizedList-test.js:

yarn test packages/virtualized-lists/Lists/__tests__/VirtualizedList-test.js

• Added test case verifying container accessibilityRole="list", aria-rowcount, item accessibilityRole="listitem", aria-setsize, aria-posinset, and accessibilityCollectionItem.

Device & Simulator Verification

• Android TalkBack: Verified screen reader announces total count on list focus and item position during navigation.
• iOS VoiceOver: Verified VoiceOver reads list container bounds and item indices.

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