[generator] Ensure "global::" is prepended to generic return casts.

[jpobst]

Context: dotnet/android#5894

When creating the cast from a generic type parameter (which is currently always JLO), global:: is not prepended to the type cast.

return (Java.Lang.Object) global::Java.Lang.Object.GetObject<global::Java.Lang.Object> (__rm.Handle, JniHandleOwnership.TransferLocalRef);

This creates a compilation error if the bound type is in a namespace that ends in "Java", like "MyProduct.Java".

Error CS0234: The type or namespace name 'Lang' does not exist in the namespace 'MyProduct.Java'.

Fix this by ensuring the cast output goes through our standard type formatting method which adds global:: when needed.