Move ReactFabricPublicInstance out of the Renderer directory

Summary:
The `Renderer` directory is supposed to be only for files synced from the React repo. This moves the `public` directory that was added to it recently to the `ReactNative` directory.

Changelog: [internal]

bypass-github-export-checks

Reviewed By: sammy-SC

Differential Revision: D44421951

fbshipit-source-id: d098970b80cd467b5c772c3ae91ce716be373484