[tests] Fix flaky tests

[nan-li]

Description

One Line Summary

Fix flaky tests so the CI can be meaningful.

Details

Add OneSignalOSCoreMocks module

• Reset the Operation Repo between tests

Introduce 2 separate Test Plans

• There are now two Test Plans in the UnitTestApp, a UnitTestApp_TestPlan_Full which is the Default test plan and can be run in Xcode, and a UnitTestApp_TestPlan_Reduced with concurrency tests disabled that is run by the CI script.

Other Misc Changes

• Move concurrency tests into 1 file
• Add some more "waits" related fixes in tests
• Fix bug that didn't clear user defaults between tests

Motivation

Fix flaky tests so the CI can be meaningful.

Scope

Tests

Testing

Unit testing

• See PR description, since PR is about tests.
• Ran CI 9 times in a row

Manual testing

Minimal

Affected code checklist

• [ ] Notifications
  • [ ] Display
  • [ ] Open
  • [ ] Push Processing
  • [ ] Confirm Deliveries
• [ ] Outcomes
• [ ] Sessions
• [ ] In-App Messaging
• [ ] REST API requests
• [ ] Public API changes

Checklist

Overview

• [x] I have filled out all REQUIRED sections above
• [x] PR does one thing
• [x] Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• [x] I have included test coverage for these changes, or explained why they are not needed
• [x] All automated tests pass, or I explained why that is not possible
• [x] I have personally tested this on my device, or explained why that is not possible

Final pass

• [x] Code is as readable as possible.
• [x] I have reviewed this PR myself, ensuring it meets each checklist item

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This change is 

[nan-li]

After 9 consecutive CI successful runs, the 10th failed on a test I am pushing a commit for. Re-running CIs.

NVM, that commit made it worse, removed it.