Fix the serialization of the alpha channel in the rgba() color string format (#52087)

Summary:
The alpha channel in the `rgba()` color string format should be a value between [0, 1] instead of [0, 255], as stated in the [React Native Documentation](https://reactnative.dev/docs/colors#red-green-blue-rgb).

## Changelog:

[GENERAL] [FIXED] - Fix the serialization of the alpha channel in the `rgba()` color string format.

Pull Request resolved: https://github.com/facebook/react-native/pull/52087

Test Plan: I didn't find any usage of that function in React Native, but it is part of the public API, and I just wanted to use it in Reanimated.

Reviewed By: fabriziocucci

Differential Revision: D76822560

Pulled By: javache

fbshipit-source-id: 370d9729881c1eda794c1b9fe54d258242fde814