Enable Windows.UI.Xaml profile for Windows SDK projections

[Sergio0694]

This PR adds support for two new profiles for the Windows SDK projections (aka "Microsoft.Windows.SDK.NET.Ref"):

• "Windows": just the Windows SDK, without anything in Windows.UI.Xaml.*
• "Full": with the entire Windows SDK (including Windows.UI.Xaml.* types)

Additionally, it includes the following changes:

• Automatically select the "Full" profile when the "UseUwp" property is set
• Error (NETSDK1216) when "UseUwp" is not set but the "Full" package is transitively referenced
• Set CsWinRT feature switch for WUX projections automatically when "UseUwp" is set

Note

Need to add tests, and we still need to publish the updated Windows SDK projections, but reviews welcome.

[dsplaisted]

This generally looks good.

It does differ from how we normally handle profiles. Normally profiles are always a subset of the full set of references for a shared framework, and a reference without a profile would be used to reference all of the references. In that model, instead of Microsoft.Windows.SDK.NET.Ref.Full, you'd just have Microsoft.Windows.SDK.NET.Ref (the same as you have today). Then you'd add Microsoft.Windows.SDK.NET.Ref.Windows for the subset without Windows.UI.Xaml.

I'm not sure if there's going to be anything wrong with the way this PR currently implements things, but if there's no specific reason to use two separate profiles, it's probably safer to keep to the existing model.

I don't remember how exactly PrivateAssets="all" behaves for FrameworkReferences. If it stops the framework reference from flowing across project references, then I think the transitive error check would never trigger. If it doesn't stop the FrameworkReference from flowing through NuGet packages, then in the current version of this PR you could have errors referencing NuGet packages which depend on the Microsoft.Windows.SDK.NET.Ref framework, which doesn't exist anymore.

[dsplaisted]

Looks good to me.

[MartinZikmund]

@Sergio0694 after updating a blank WinUI 3 .NET 8 app to WindowsSdkPackageVersion xyz.48:

<WindowsSdkPackageVersion>10.0.19041.48</WindowsSdkPackageVersion>

I am now seeing both of these are now valid:

var red = Microsoft.UI.Colors.Red;
var red2 = Windows.UI.Colors.Red;

Is that change intentional 🤔 ? Same goes for Microsoft.UI.Text.FontWeights