Don't require targetversion to be latest for Class Libraries

Describe the bug When building a class library, the target version should not matter, as long as it’s at least minversion. That check should only apply to app projects.

This check is done here and should have a condition for class libraries to ignore it (or check that target is at least minversion): https://github.com/microsoft/microsoft-ui-xaml/blob/8f8cd0fe32754cfcd83dafb2fc8539703b6aec26/build/NuSpecs/MUXControls-Nuget-Common.targets#L16-L18

Steps to reproduce the bug

1. Create a .NET Class Library and set target version to 17134.
2. Add WinUI nuget package.
3. Build

Expected behavior Build succeeds

Actual behavior Build error:

C:\Users\username\.nuget\packages\microsoft.ui.xaml\2.3.191211002\buildTransitive\Common.targets(16,5): error : Microsoft.UI.
Xaml nuget package requires TargetPlatformVersion >= 10.0.18362.0 (current project is 17134) [E:\src\myclasslibrary.csproj]

Version Info 2.3.191211002

[jevansaks]

The problem is that the WinUI metadata has types it references that weren’t introduced until a later version of the Windows SDK. You will get a bizarre compiler error about not being able to resolve types if you disable the check and target too old of a Windows SDK.

[dotMorten]

I’m ok with closing this