refactor(datastore): Add OptimisticConcurrency tests

[stocaaro]

Warning

PR reconstructed as part of a rebase - Please see #88

Description of changes

Outcomes:

• Add OptimisticConcurrency (OCC) tests for all cases covered by the existing Automerge tests
• Change test resolution so that latent tests processes subscription updates after mutation response update
  • This is more consistent with what is observed in the wild, where Datastore receives repeat updates
• Raise returned object when errors are present aligning mock behavior with the client logic it overrides.
• Wait for all subscriptions to be published before proceeding (remove a race condition between test assertions and subscription updates)

While adding OCC testing, I noticed my sample app result diverged from our test results. Investigating this led me to identify that this is substantially true for our existing Automerge tests. The difference comes from having subscription updates arrive into datastore before the mutation response is returned. This is possible, but not the common case. I have factored the latent tests towards the more common case which is has noisier redundant messages.

Description of how you validated changes

By comparing sample app results to test expectations and iterating until they align.

Related changes

1. refactor(datastore): Move conflict resolution tests to their own file aws-amplify/amplify-js#12728
2. refactor(datastore): Refactor conflict resolution tests optimize for concise/readable aws-amplify/amplify-js#12732
3. test(datastore): Refactor test names/comment and add OCC fake #85
4. 🌱 refactor(datastore): Add OptimisticConcurrency tests
5. fix(datastore): Update outbox comparison logic to fix update versioning problems #87

Checklist

• PR description included
• yarn test passes
• Tests are changed or added

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.