Investigate how much work it is to switch away from the deprecated xunit.console runner to dotnet vstest. This is just about the runner, the test infra backend will still be xunit.

UAP will continue using Microsoft.DotNet.XUnitRunnerUap.
UAPAOT is problematic. We currently use xunit.console for it which doesn't work (https://github.com/dotnet/corefx/issues/30423). It may be our best option to add a ifdef configuration in dotnet/arcade#1627 which works fine with uapaot.