Explore the full inheritance/interface graph

[paulproteus]

Right now, rubicon-java only looks at the immediate interfaces a class implements along with its superclasses. ArrayAdapter in Android fails to find SpinnerAdapter, so we have to do this ugly hinting.

https://github.com/beeware/toga/pull/905/files#diff-2a4e44cc48a82e70ea678ecb88a8a66fR23

# Indicate to `rubicon-java` that `ArrayAdapter` can also be typecast into a
# `SpinnerAdapter`. This is required until `rubicon-java` explores the interfaces
# implemented by a class's subclasses.
ArrayAdapter._alternates.append(b'Landroid/widget/SpinnerAdapter;')