CLI Testing via msbuild (#3779)

* Rebase

* Remove Multi-Project Validator

* Remove projectmodelserver tests

* Enable test package creation

* Incremental test restore

* WiP

* Enable Test Asset Project restore

* Build Test Assets & Restore Test Projects

* Build Test projects

* Enable Test Execution

also moves Test Targets to a well-known CLI Version [Stage 2]

* Pass throuh existing telemetry profile

* 2-space tabs

* Revert TestTargets.cs

* WiP PR feedback

* Refactoring

* Fix naming of RestoreTestAssetPackages

* DotNetTest task

* Fix merge issue

* ExecuteWithCapturedOutput

MSBuild considers StdErr output to be failures. This causes output of any test command which is expected to produce an error to be swallowed in the test.

* Workaround for always-on tracing functionality in dotnet-test

* Fix Path Separator Windows/Unix

* Seperate package build from pack

* Windows Pathing issues

* PR Feedback

* Workaround for msbuild #773

https://github.com/Microsoft/msbuild/issues/773

test/dotnet.Tests/GivenThatDotNetRunsCommands.cs

@@ -18,7 +18,7 @@ namespace Microsoft.DotNet.Tests
 
             new RestoreCommand()
                 .WithWorkingDirectory(testInstance.TestRoot)
-                .Execute()
+                .ExecuteWithCapturedOutput()
                 .Should()
                 .Fail();
             new DirectoryInfo(testInstance.TestRoot)