Changes to prepare for consolidation

[jkoritzinsky]

• Define a SetupRoot MSBuild property to represent the root of the core-setup repo. It will point to the root folder of the core-setup files in the consolidated repo.
• Make some projects SDK projects so they pull in Directory.Build.props/Directory.Build.targets.
• Make the root directory configurable for the native build.
• Rename LICENSE.TXT to LICENSE to match the final name in the consolidated repo.
• Add MSBuild property definitions to configure the Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk for this repo and the consolidated repo.

[dagood]

Scanned through it again, LGTM. 🎉

[jkoritzinsky]

Looks like I might have missed a spot in the Arcade SDK. I'll put out a PR there to fix the issue.

[jkoritzinsky]

Actually the SDK version hasn't been updated yet. That should be automatic... I'll update it manually.

[dagood]

Hmm... I submitted a PR to Maestro++ a while ago to enable auto-updates for this SDK. I'll see why that isn't (apparently) working. dotnet/arcade-services#662

[ViktorHofer]

LGTM. Thanks a lot for the quick backporting.

[ViktorHofer]

The renaming of the LICENSE.TXT to LICENSE needs to be revert asap if the Microsoft.NETCore.App assets (package, ...) are hard-linking to this file. cc @dagood @jkoritzinsky

[ViktorHofer]

we can keep the LICENSE.TXT name anyway, initially I thought the renaming is necessary for GH to detect the right license but that was wrong.

[dagood]

Yes, the license link on https://www.nuget.org/packages/Microsoft.NETCore.App.Ref/3.0.0 (and probably more) is a 404 now: https://github.com/dotnet/core-setup/blob/master/LICENSE.TXT. I'll put up a PR.