Improve how Azure DevOps extensions identifies interesting stack trace entries

[nohwnd]

Describe the bug

#5260 (comment)

The extension is now relying on MSTest to provide a filtered stack trace and just takes the first line.

This is not the desired state, we need to find the first entry that belongs to a code file in the repository, which gives us the best chance of reporting the error back to github PR (via the standard AzDo integration).

Look at how TFS DistributedLogger for msbuild does it, and possibly figure out better ways to provide the repository root. (e.g. if we move the run to a different server we won't be able to find the .git folder, so we need to provide it externally, or as a glob *MyProject/src.

Steps To Reproduce

Use the extension with xunit and see it fail to report the error back to GH (most likely).