Add conic gradients to View backgroundImage

[Stringsaeed]

Summary:

TL;DR

Adds conic-gradient() support to View's backgroundImage style on iOS and Android.

Supported syntax includes:

• from <angle>
• at <position>, including four-value edge offsets
• angular and percentage color stops
• two-position color stops
• transition hints
• string and object style syntax
• multiple background-image layers

Implementation

• Extends the JavaScript and native C++ background-image parsers.
• Adds a shared ConicGradient graphics model and serialization.
• Uses CAGradientLayer with kCAGradientLayerConic on iOS.
• Uses SweepGradient on Android.
• Reuses existing background sizing, positioning, repeat, border, and clipping infrastructure.

Reviewer guide

Recommended order:

1. Parser and model:
   • processBackgroundImage.js
   • CSSBackgroundImage.h
   • ConicGradient.h/.cpp
2. Prop conversion:
   • BackgroundImagePropsConversions.cpp
3. Platform rendering:
   • RCTConicGradient.mm
   • Android ConicGradient.kt
4. Tests and RNTester examples.
5. ReactNativeApi.d.ts is generated and can be reviewed mechanically.

Scope

This PR does not add:

• repeating-conic-gradient()
• CSS color-interpolation methods such as in hsl
• explicit normalization for stops outside the visible 0–360 degree interval

Changelog:

[GENERAL] [ADDED] - Support conic gradients in View backgroundImage.

Test Plan:

• yarn flow-check — 0 errors
• yarn test-generated-typescript — passed
• Focused ESLint and Prettier checks — passed
• yarn fantom packages/react-native/Libraries/StyleSheet/__tests__/processBackgroundPosition-itest.js — 80 tests passed
• yarn fantom packages/react-native/Libraries/StyleSheet/__tests__/processBackgroundImage-itest.js — 77 tests passed
• yarn fantom packages/react-native/Libraries/Components/View/__tests__/View-nativeCSSParsing-itest.js — 6 tests passed
• yarn fantom packages/react-native/Libraries/Components/View/__tests__/View-itest.js — 224 tests passed across native CSS parsing and C++ prop setter flags
• Native Fantom C++ target — built successfully
• ./gradlew :packages:rn-tester:android:app:assembleDebug — built successfully
• RNTester on iOS simulator — verified clockwise quadrant orientation, from rotation, and off-center at positioning

Known merge-readiness issue

The change introduces public C++ API surface, but C++ API snapshots are not updated. Local generation fails on Android views with an existing duplicate fmt::v12::basic_appender parser error. Regenerate those snapshots in the supported Linux CI environment before final review.

[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