Presently we're looking if enums decorated with [Native] are used, just
like we do for p/invokes and delegate types decorated with a
[MonoNativeFunctionWrapper] attribute.
Testing properly required to add a property to MonoPInvokeCallbackAttribute
so we can get back the type given as it's argument.
* Also check for generics in delegates, ref: #42699
* Ignore failures filed as https://bugzilla.xamarin.com/show_bug.cgi?id=53058
Those tests needs to be run with the linker disabled since they use
reflection for most of their work.
The original dontlink (for linker tests) was becoming too large in
some configuration (e.g. tvOS release with bitcode) but this was
due to other BCL assemblies (not the introspection tests)