Reorganise shared script utils (#52473)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/52473

Shared utils that were located in the root of `scripts/` are now colocated closer to their dependencies or moved to `scripts/shared/` — simplifying the root directory layout.

Changelog: [Internal]

Reviewed By: robhogan

Differential Revision: D77873875

fbshipit-source-id: e04dba41a1ef811d32793931033fdfa93afad0cd