Arcade does not include xunit.runner.json file if being run with the VS Test runner

[jmarolf]

• [ ] This issue is blocking
• [X] This issue is causing unreasonable pain

If a consumer of arcade sets <UseVSTestRunner>true</UseVSTestRunner> like we do here.

This causes all xunit targets to be skipped: https://github.com/dotnet/arcade/blob/6cc4c1e9e23d5e65e88a8a57216b3d91e9b3d8db/src/Microsoft.DotNet.Arcade.Sdk/tools/XUnit/XUnit.targets#L18-L19

as a result any configuration such as a custom xunit.runner.json are not respected. The following sections should be moved from XUnit.Runner.targets ot XUnit.targets

https://github.com/dotnet/arcade/blob/6cc4c1e9e23d5e65e88a8a57216b3d91e9b3d8db/src/Microsoft.DotNet.Arcade.Sdk/tools/XUnit/XUnit.Runner.targets#L2-L4

https://github.com/dotnet/arcade/blob/6cc4c1e9e23d5e65e88a8a57216b3d91e9b3d8db/src/Microsoft.DotNet.Arcade.Sdk/tools/XUnit/XUnit.Runner.targets#L10-L24

[garath]

This looks like work as part of the unification effort we want to get to, but this work is not prioritized. If you want to submit a PR in the meantime, we'd be happy to look at it.

[JoeRobich]

Implemented Jon's suggestions in https://github.com/dotnet/arcade/pull/7170