Centralize path definitions for Fantom builds and move to .out (#52829)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/52829

Changelog: [internal]

Just a small refactor to move the definitions of output paths to a specific module. We'll add more to this in a latter diff.

Reviewed By: sammy-SC

Differential Revision: D78905645

fbshipit-source-id: 011e6cec13396301dad8e76400b6f2b9e13568f0