Add kotlin property assignment test case

[donat]

fyi @asodja

[asodja]

Nice! 🎉

Since we have also ConfigurableFileCollection.assign(fileCollection: FileCollection) and assign methods for ListProperty/SetProperty/MapProperty, consider adding additional properties to GreetingTask like:

val cfc: ConfigurableFileCollection
// List and Set have the same extensions, so we probably don't need to test both
val listProperty: ListProperty<String>
val mapProperty: MapProperty<String>

and have some assignments for them. Here you can find defined property assign methods and for cfc assign methods.