Migrate Libraries/Utilities/*.js to use `export` syntax. (#48665)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/48665

## Motivation
Modernising the react-native codebase to allow for ingestion by modern Flow tooling

## This diff
- Updates files in Libraries/Utilities to use `export` syntax
  - `export default` for qualified objects, many `export` statements for collections (determined by how it's imported)
- Appends `.default` to requires of the changed files.
- Updates Jest mocks of the `Platform` module, which happened to touch a lot of test files.
- Updates the public API snapshot (intented breaking change)

Changelog:
[General][Breaking] - Files inside `Libraries/Utilities` use `export` syntax, which requires the addition of `.default` when imported with the CJS `require` syntax.

Reviewed By: huntie

Differential Revision: D68152910

fbshipit-source-id: 07f3a0957f1dbaf44f53974c6f28b273558406eb