Add ability to capture failed test outut for Xunit#555

AngryTester95 wants to merge 2 commits intoallure-framework:mainallure-framework/allure-csharp:mainfrom

AngryTester95:feature/xunit-handle-output-for-failed-testsAngryTester95/allure-csharp:feature/xunit-handle-output-for-failed-testsCopy head branch name to clipboard