fix: export feature flags for virtualized lists

[CHANDRAMOHANnegi]

Summary:

Fixes #57933.

PR #57484 removed the broad ./src/* export from the react-native package. However, the published @react-native/virtualized-lists package still imports ReactNativeFeatureFlags through an unexported subpath. This causes Metro to emit a package-exports warning when applications render a FlatList.

This change exposes only the exact feature-flags subpath required by VirtualizedList, without restoring the broad ./src/* export. It also adds a regression test verifying that the import resolves through the package exports map.

Changelog:

[General] [Fixed] - Fix Metro package-exports warning when using VirtualizedList

Test Plan:

• yarn test package-exports-test --runInBand
  • 1 test passed.
• yarn test VirtualizeUtils-test --runInBand
  • 17 tests passed.
• yarn lint packages/virtualized-lists/Lists/__tests__/package-exports-test.js
  • Passed.
• git diff --check
  • Passed.

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