[Genernal] Added slash of alpha support using rgb()

[zhongwuzw]

Summary:

Fixes #50207

Added slash alpha support like rgb(255 122 127 / 0.2);, currently seems we don't support it.

Changelog:

[GENERAL] [ADDED] - Added slash of alpha support using rgb()

Test Plan:

rgb(255 122 127 / 0.2) can shows correctly.

[NickGerleman]

CSS colors module level 4 also allows rgba() to not contain alpha. We could unify these paths. https://www.w3.org/TR/css-color-4/#rgb-functions

rgb() legacy syntax (using comma) is also allowed to contain alpha.

Another existing bug here, is that we shouldn't allow slash notation at all when using comma separator, but existing regex supports this.

All of this will eventually get replaced in new arch by https://github.com/facebook/react-native/blob/main/packages/react-native/ReactCommon/react/renderer/css/CSSColorFunction.h but this is further out. Making fixes to existing impl like this makes sense to me.

[zhongwuzw]

@NickGerleman Please review again.

[facebook-github-bot]

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

[facebook-github-bot]

@NickGerleman merged this pull request in 7441127.