User projects always download WinUI 3 Preview NuGet package (~130MB)

[NickGerleman]

To repro, build the 0.63 Calculator sample in react-native-windows-samples repo.

The Microsoft.WinUI.3.0.0-preview2.200713.0 package is pulled in, possibly because the Microsoft.ReactNative project requires it in packages.config.

Affects multiple versions. I.e. not a new regression.

[NickGerleman]

FWIW, if we've had it there and nobody has been complaining, a different option is to explicitly take the hit to simplify logic around maintaining NuGet packages.

[chrisglein]

Won't be pulled in for the build, but will be downloaded. There isn't a mechanism for Visual Studio to have this conditional on something. It's possible we could create a custom solution here. It'd be nice to reduce our footprint.