Add AccessibilityInfo.getContrastLevel and contrastLevelChanged on Android

[camilopires]

Summary:

Android 14 (API 34) added a system contrast level (Settings → Accessibility → Color and motion → Contrast), from -1 to 1, read with UiModeManager.getContrast(). It is Android's equivalent of iOS Increase Contrast, which React Native already exposes as isDarkerSystemColorsEnabled(). The existing Android method, isHighTextContrastEnabled(), reads a different setting that only changes how text is drawn.

This adds AccessibilityInfo.getContrastLevel(): Promise<number> and a numeric contrastLevelChanged event, for Android only.

• A ContrastChangeListener is registered while the app is resumed, and removed on pause and in invalidate().
• The value is read again on resume, because registering doesn't report the current value.
• The listener is created lazily, so older Android versions never load the API 34 interface.
• On Android before 14 and on iOS, the method resolves to 0.
• The TypeScript declarations add an addEventListener overload, because this event's payload is a number rather than a boolean.

RNTester gets a small example that shows the value and the last event's payload.

Discussion: react-native-community/discussions-and-proposals#1026

Changelog:

[ANDROID] [ADDED] - AccessibilityInfo.getContrastLevel() and contrastLevelChanged (Android 14+ contrast level)

Test Plan:

• yarn jest packages/react-native/Libraries/Components/AccessibilityInfo: all tests pass
• yarn flow-check: 0 errors
• yarn lint: passes
• yarn build-types --validate: API snapshot up to date
• yarn test-generated-typescript and yarn test-typescript-legacy: pass
• yarn format-check-kotlin: passes
• RNTester builds: ./gradlew :packages:rn-tester:android:app:assembleDebug

RNTester on an Android 16 (API 36) emulator:

• Getter: adb shell settings put secure contrast_level with 0, 0.5, 1.0 and -0.5 gave "Contrast level is 0." / "0.5." / "1." / "-0.5."
• Events: Android recreates the activity when the contrast changes, so I logged the listener temporarily, locally and not in this PR. Setting 0.25, -0.75 and 0.0 logged contrastLevelChanged with exactly 0.25, -0.75 and 0, all in the same process.
• Changed while in the background: set 0.75, then brought the app back. The row showed "Contrast level is 0.75."

RNTester on an Android 10 (API 29) emulator: "Contrast level is 0.", with no crashes across launch and resume.

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[github-actions]

Warning

JavaScript API change detected

This PR commits an update to ReactNativeApi.d.ts, indicating a change to React Native's public JavaScript API.

• Please include a clear changelog message.
• This change will be subject to additional review.

This change was flagged as: POTENTIALLY_BREAKING

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@javache has imported this pull request. If you are a Meta employee, you can view this in D126038114.