On test failure, report more context from the logs to the Azure Pipeline report

[kmahone]

When a test failure occurs, we report the results back to Azure Pipelines. The 'Tests' tab of the Pipeline shows the failing tests and an error message for each.

Currently, the error including 'Warnings' and 'Errors' from the test log. Often this is hard to interpret since it is missing so much context. See this test run for an example: https://microsoft.visualstudio.com/WinUI/_build/results?buildId=13356842&view=ms.vss-test-web.test-result-details

I tried including the full test log output, but the Error Message string gets truncated.

It is possible to get to the full test logs on Mission Control, but this requires a bunch of clicking through various links and it also gives you the complete log for the entire run (i.e. every test in the test class).

The best approach would probably be to report the Error Message to Azure Pipeline as the error log output pre-pended with the last few lines of standard output just before the error. This should be fairly easy to add to ConvertWttLogToXUnit.ps1 and would make interpreting the test reports a lot easier.

[kmahone]

Completed: #176