Describe the bug
I can't use this library from another library that references AnyCPU.
There's no reason why this library can't be used by an AnyCPU library, except you have a build task preventing me from doing that.
You also require MinVersion and Version to be 14393 and 17763, which again shouldn't matter for class libraries.

Steps to reproduce the bug

1. Create an AnyCPU class library.
2. Reference this package.
3. Build

Expected behavior
Build completes.

Screenshots

Version Info
Win10, 1809, VS2019.

NuGet package version:
2.1.190405004

Additional context
The build error is valid for app-heads, but not class libraries.

I also believe a similar check be done to the MicrosoftUIXamlCheckTargetPlatformVersion Target, which shouldn't run on class libraries, but only app-heads.
Also to ensure these build files gets run on on app-heads when indirectly references, the entire \build\ folder should be duplicated to the transitiveBuild folder.