Add `PlatformColor` module

[luixo]

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Describe the feature request

Hello,
There's a module PlatformColor in react-native
As react-native ecosystem is too big, a lot of community package developers don't check if a specific module exists in web counterpart of the react-native.

In my case this resulted into nativewind v5 not being able to compile by vite because it relies on the PlatformColor module.

Adding this as an identity function will help a lot (though getting system color would be a better alternative).

This was already open, but closed for technical reasons.

I'm up for a PR, let me know if that PR will be considered to merge.