Re-enable C++/CLI tests

[wli3]

C++ does not support package restore. So, it is cannot download apphost pack from the internet. Since I made a change recently to use stage 2 bundled version props file instead of stage 0 (to avoid needing to update stage 0 when runtime insert), apphost will not be in the "dotnet" folder. The solution could be, in the test set up, download the missing apphost pack. But that will duplicate a lot of dotnet/installer code. Or move these tests to dotnet/installer.

[wli3]

Or overriding the implicit versions during the test themselves

[Nirmal4G]

Why not use PackageDownload?

[wli3]

C++/CLI project system does not support PackageDownload. And PackageDownload uses nuget