Update ShowMeTheXAML to version 2.0.0

[Keboo]

ShowMeTheXAML just released a new 2.0.0 with some breaking changes.
The key differences is the Key properties on the XamlDisplay class was renamed to UniqueKey. We should update the version we are using to 2.0.0 and update all of the usages to using the new property.

These dependencies are managed with Paket not NuGet directly so you will need to use paket to update and restore the dependency. Keep in mind there is a separate issue for updating paket (#2118) so the exact command needed will depend on if that work has been done.

[jespersh]

@Keboo what should one expect from this Uno.UI dependency defined in the nuspec file of SMTX?

      <group targetFramework=".NETStandard2.0">
        <dependency id="Uno.UI" version="3.0.17" exclude="Build,Analyzers" />
      </group>

[Keboo]

The netstandard dependency should not be picked up by WPF since the .NET Framework and NET Core App dependencies should be a better match. I would not expect that to affect this project.