Make Desktop WPF use Core WPF targets and tasks (MarkupCompile)

[KirillOsenkov]

Currently when you build a WPF application for net472 and use legacy WPF, it imports C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Xaml.targets:

The targets are legacy and haven't been updated. For example, GenerateTemporaryTargetAssembly task doesn't have the latest properties:

We need to stop relying on things from C:\Windows, for hermetic and isolated builds. Moving to the same targets and tasks in the SDK instead ensures portability (you could build WPF desktop projects on Mac, for example) and future-proofs them.

Bonus: see if it's possible to use the new WPF assemblies for net472 desktop applications, instead of the ones shipping in .NET Framework. If possible, this would allow to prepare WPF apps for moving to .NET Core.