Sample projects don't allow for WinUI 2/3 dependencies

[Arlodotexe]

Background

In #132, we gave Lab libraries the ability to declare dependencies under UWP, WinAppSdk and Uno under both WinUI 2 and 3.

The problem

However, we didn't provide a way for sample projects to declare dependencies the same way. This means that if a sample project needs a nuget package that uses WinUI, they would need to add it to their lab source project, even if that project never used it, or in the case of netstandard projects, can't use it.

The solution

Allow sample projects to include WinUI 2/3 dependencies in the same way as #132 did for library projects.