RN: Refactor Jest Default Mocks (#51669)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/51669

Refactors the default mocks initialized in `packages/react-native/jest/setup.js` so that each mock is defined in its own file.

This provides several benefits, including:

- The ability to use `import` statements without worrying about eager initialization of dependencies before `globals` is setup.
- The ability to verify mocks export the same types as the actual module, using a new Flow-typed `mock` helper function.
- The ergonomic of implementing mocks with more complex logic, without having to split them out into a separate module (e.g. `mockModal`, `mockScrollView`).

As part of this migration, I also fixed any minor discrepancies to match the actual type definition. For more involved discrepancies (e.g. missing methods), I added type suppressions for now to minimize breaking changes.

Changelog:
[General][Changed] - Improved default mocking for Jest unit tests.

Reviewed By: javache

Differential Revision: D75575421

fbshipit-source-id: 98d60e10b753f1505ffdccf5f12f5d3ef306ebb5