Support emitting a results file with failures, which can be consumed by the arcade test results exporter

The arcade test results reporter publishes the results to azdo, so the errors can be seen from the UI. The currently generated reports are not compatible, and don't show execution errors.

Instead, we should generate a xunit style test results xml with just the failures. The execution errors can be accessed from `report.ExecuteResults` -> `ExecuteResult.Data` (related https://github.com/dotnet/BenchmarkDotNet/pull/2096). This would make it easier to find, and track errors in kusto, or surfacing them in `Build Analysis` on PRs, or directly looking at the details in azdo instead of going to the console log, and then trying to find the failures in that.

cc @adamsitnik @LoopedBard3 @DrewScoggins