feat: unify platform specific high contrast APIs to AccessibilityInfo.isHighContrastEnabled

[Saadnajmi]

Summary:

Every platform has some form of "high Contrast", with a separate React Native API to access it. These all do the same thing, query the OS to see if its version of "high contrast" is enabled, and report it back to AccessibilityInfo. Sadly, each platform (Android, iOS, macOS, Windows) used their own platform specific name to read this in JS.

• On Android, it's isHighTextContrastEnabled, introduced in RN 0.77 with d4ea147
• On iOS, it's isDarkerSystemColorsEnabled, introduced in RN 0.77 with af3bee6
  • Sidenote: this API natively seems to be superseded by accessibilityContrast. Luckily, inspecting UIKits headers tells me the two should report the same info most of the time.
• On macOS, we chose isHighContrastEnabled which is at least as old as RNM 0.66 but probably older
• On Windows, it's AppTheme.isHighContrast, which I'm not sure how old it is.
  • Sidenote: The inspiration for this PR was to introduce an API to AccessibilityInfo upstream of React Native macOS and Windows so they both could implement it and in the new architecture, we would have a simpler API.

This leads to real divergences in product code, where we must fork our JS per platform to do essentially the same thing (see microsoft/react-native-gallery#470 for an example).

Let's unify the APIs under a single isHighContrastEnabled API. A bit cheeky I chose the API name from the fork of React Native I maintain (React Native macOS), but I do think it's the most coherent name.

To help migration, I added a deprecation warning to the iOS and Android APIs. The idea being

• RN 0.79: Add the new API, deprecate the old ones
• RN 0.80+: Remove the old ones
  so that users have time to migrate

Changelog:

[GENERAL] [ADDED] - Add isHighContrastEnabled to AccessibilityInfo

Test Plan:

I updated the AccessibilityExample page on RNTester with both the old and new API.
On both Android and iOS, the new API matches the old API when high contrast is enabled through system settings

Screen.Recording.2025-03-12.at.5.02.11.AM.mp4

[facebook-github-bot]

@jorge-cab has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.