test(flushPromiseQueue): deprecate flushPromiseQueue and give some examples

[araujobarret]

This PR deprecates flushPromiseQueue and shows some examples how to proper handle these cases within some test scenarios.

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Description

PR Checklist

• [ ] I have tested my changes on iOS and Android.
• [ ] I hid my changes behind a feature flag, or they don't need one.
• [ ] I have included screenshots or videos, or I have not changed the UI.
• [ ] I have added tests, or my changes don't require any.
• [ ] I added an app state migration, or my changes do not require one.
• [ ] I have documented any follow-up work that this PR will require, or it does not require any.
• [ ] I have added a changelog entry below, or my changes do not require one.

To the reviewers 👀

• [ ] I would like at least one of the reviewers to run this PR on the simulator or device.

Changelog updates

### Changelog updates #### Cross-platform user-facing changes - #### iOS user-facing changes - #### Android user-facing changes - #### Dev changes -

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[ArtsyOpenSource]

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