Add logic to copy headers to .framework (#49433)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/49433

This change adds the logic to copy the Headers files from the dependency folder to the generated frameworks folder.

There is a slight possibility that this function will be implemented by the Swift PM build system, as I open [this question](https://forums.swift.org/t/xcodebuild-does-not-generate-headers-if-the-source-is-swift-pm/77856) on the Swift forums.

In that case, we would be able to drop this.

## Changelog:
[Internal] - Add function to copy headers over to the .frameworks

Reviewed By: cortinico

Differential Revision: D69656046

fbshipit-source-id: e9d4f0f53ea57bc0df86fc9194cdf9fc1f372730