feat(JS): background-size, position and repeat styles

[intergalacticspacehighway]

Summary:

This PR adds support for background size, position and repeat styles. It follows the CSS spec. Currently we default to background-origin: padding-box and background-clip : border-box to match the web's behavior. We can introduce these styles later. I have split the PR intro three parts for review. This PR includes JS parsing and style propagation to native changes. I wanted to introduce one style at a time, but CSS spec is such that size, position and repeat are intertwined.

Changelog:

[GENERAL][ADDED] - Background size, position and repeat styles.

Test Plan:

Merge the iOS and android PR into this, this PR includes BackgroundImageExample. I have also added testcases for parsing syntax in JS.

Screen.Recording.2025-06-26.at.10.47.17.AM.mp4

[javache]

I think we want to do this parsing in native using the new CSSParser infra, and not rely on JS viewconfigs.

cc @NickGerleman

[intergalacticspacehighway]

yeah, i wanted to mention that. Is it in use already?

[javache]

Seems like it's still gated behind a feature flag for now:

react-native/packages/react-native/ReactCommon/react/renderer/components/view/BoxShadowPropsConversions.h

Lines 265 to 274 in c660868

	inline void fromRawValue(
	const PropsParserContext& context,
	const RawValue& value,
	std::vector<BoxShadow>& result) {
	if (ReactNativeFeatureFlags::enableNativeCSSParsing()) {
	parseUnprocessedBoxShadow(context, value, result);
	} else {
	parseProcessedBoxShadow(context, value, result);
	}
	}

[javache]

Actually, just reading through some of the history there, until we complete another refactor on Android, we will still need JS parsing of these types there.