Migrate xUnit plugin. (#27)
* Migrate xUnit plugin.
* Remove redundant GitContext class
* Changed target framework for shared library, moved TestCase to shared location.
* Remove old models, simplify test case collection.
* Moved NUnitTestCasePayload to shared library.
* Rewriting TestResultsBuilder
* Fixed typo in enum name.
* Fleshed out rest of reporting.
* Added reference link for NUnit TestCase XML definition.
* Made xUnit package target netstandard2.0 instead of net6
* Moved some tests.
* Renamed to match new type name.
* Added some sample xUnit tests to publish.
* Refactoring to clean up task contention (attempting to run binary inside a task).
* Fixed async issues, testing generated JSON again.
* Fixing how we populate the name
* Removed testing code.
* Code cleanup, remove random tests.
