RN: Refactor Jest Default Mocks

[yungsters]

Summary: 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.

Differential Revision: D75575421

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This pull request was exported from Phabricator. Differential Revision: D75575421

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75575421

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75575421

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75575421

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75575421

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75575421

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75575421

[facebook-github-bot]

This pull request has been merged in facebook/react-native@1fd9508ecc499df89b086e0c46035f43f6f78ad9.

[react-native-bot]

This pull request was successfully merged by @yungsters in 1fd9508ecc499df89b086e0c46035f43f6f78ad9

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