Route virtualized-lists feature flags through react-private-interface

[giaBaoJS]

Summary:

Fixes #57933.

@react-native/virtualized-lists is published separately and used to import ReactNativeFeatureFlags through the unexported path react-native/src/private/featureflags/ReactNativeFeatureFlags. Metro therefore warned and fell back to file-based resolution whenever an app rendered a virtualized list.

Following the maintainer's suggested direction, this PR now:

• exposes ReactNativeFeatureFlags from the existing private package boundary, react-native/react-private-interface;
• routes both runtime consumers (VirtualizedList.js and VirtualizeUtils.js) through that boundary; and
• keeps the generic monorepo guard that rejects runtime deep imports from published packages when the target subpath is not exported.

This avoids exposing any new src/private/* subpath while preserving the existing feature-flag singleton.

The four similar imports in @react-native/jest-preset remain out of scope because they are all import type and are erased before resolution.

Changelog:

[GENERAL] [FIXED] - Fix the Metro package-exports warning caused by @react-native/virtualized-lists importing an unexported React Native subpath.

Test Plan:

The regression test is intentionally independent of Jest's patched resolver: it reads the package exports map directly and checks runtime imports shipped by published workspace packages.

Counterfactual with the final test kept but only the two virtualized-lists imports reverted:

FAIL package exports › published packages must only deep import exported react-native subpaths

@react-native/virtualized-lists: Lists/VirtualizeUtils.js imports
'react-native/src/private/featureflags/ReactNativeFeatureFlags',
which is not listed in react-native's \"exports\"

@react-native/virtualized-lists: Lists/VirtualizedList.js imports
'react-native/src/private/featureflags/ReactNativeFeatureFlags',
which is not listed in react-native's \"exports\"

Restoring the private-interface imports makes the same test pass.

After rebasing onto current main:

yarn test scripts/monorepo-tests/__tests__/check-packages-test.js \
  packages/virtualized-lists/Lists/__tests__/VirtualizedList-test.js \
  packages/virtualized-lists/Lists/__tests__/VirtualizeUtils-test.js --runInBand

3 suites passed
106 tests passed / 1 skipped
59 snapshots passed

yarn flow-check
Found 0 errors

yarn lint
Done (0 warnings, 0 errors)

[huntie]

Great spot! We'll need to solve this slightly differently however, I think by adding this API to react-private-interface.

import {ReactNativeFeatureFlags} from 'react-native/react-private-interface';

Patch here: https://gist.github.com/huntie/0523e2dd114dacf904d28211ad6b67be. Can you apply/retitle this PR to match? :)

[huntie]

Can we drop or separate out the changes from this file?

At minimum, we've reimplemented ESLint and should instead reuse it — should be a case of enabling the react-native/no-deep-imports rule directly on the virtualized-lists codebase. (But also, we're probably fine without adding new checks.)