MSTest v3

[Haplois]

Work In Progress

Initial refactoring of MSTest code base for MSTest v3.

• [x] Convert all projects to Microsoft.NET.Sdk style.
• [x] Separately package WinUI and UAP support as an extension package.
• [x] Add or remove TFMs make supported platforms as: net462, netstandard1.4, netstandard2.0, and net5.0; also adding support packages for UWP and WinUI.
• [x] Full arcade conversion
• [ ] Port tests
• [ ] Simplify MSBuild scripts included in our packages.
• [ ] Reintroduce SytleCop rules

These are not in the scope of this PR

• Remove Microsoft.TestPlatform.ObjectModel dependency if possible
• Discuss moving away from .runsettings if possible
• Update documentation
• net5.0 and newer frameworks doesn't support Thread.Abort() behavior which we use to cancel tests. We can probably implement it using PInvoke discuss its necessity.
• Add more integration tests to test all supported platforms