SupportedTargetFrameworkAlias.xaml not found on disk at runtime

Seen when debugging the .NET Project System:

```
CPS Information: 12552 : Loading schema file: D:\repos\project-system\artifacts\Debug\VSSetup\Rules\SupportedTargetFrameworkAlias.xaml
CPS Warning: 12552 : Failure loading XAML file 'D:\repos\project-system\artifacts\Debug\VSSetup\Rules\SupportedTargetFrameworkAlias.xaml': File cannot be found
```

`SupportedTargetFrameworkAlias.xaml` does not exist on disk at that location.

We embed this rule, apparently:

https://github.com/dotnet/project-system/blob/02033da2c6e238403885f6ec1bb6995f83dc2c2b/src/Microsoft.VisualStudio.ProjectSystem.Managed/ProjectSystem/Rules/RuleExporter.cs#L26-L33

There must be something wrong with the configuration of this rule in our code that's causing it to search the disk rather than find it embedded.