WindowsDesktop shared framework should add PackageOverrides.txt

[ericstj]

Description

The PackageOverrides.txt file provides a fast-path for conflict resolution and may also serve as an input to package pruning. @dsplaisted @nkolev92

WindowsDekstop should provide this in the targeting pack, similar to what Runtime and AspNet do: https://github.com/dotnet/runtime/blob/fa0f65c9a89cd140929aa12ac3ab70d2d0fc0d6d/src/installer/pkg/sfx/Microsoft.NETCore.App/Directory.Build.targets#L18-L36
https://github.com/dotnet/aspnetcore/blob/28bad7ae10cb640ae393f7d3f53fb7e298a8765d/src/Framework/App.Ref/src/Microsoft.AspNetCore.App.Ref.sfxproj#L146-L175

As done with those repos, this file can be generated. Per dotnet/sdk#44566 this file (and other conflict resolution data) should track the latest versions rather than GA.

cc @dsplaisted @ViktorHofer