Reduce code duplication by making a few classes extend AbstractRichIterable.

[motlin]

Reduce code duplication by making a few classes extend AbstractRichIterable, including:

• ImmutableArrayStack
• primitiveObjectHashMap
• abstractImmutablePrimitiveObjectMap
• immutablePrimitiveObjectHashMap
• MutablePrimitiveObjectMap

[kedar-joshi]

ImmutableArrayStack<T> implements ImmutableStack<T> which conflicts with AbstractRichIterable<T> at least for countByEach(Function<? super T, ? extends Iterable<V>>).

MutablePrimitiveObjectMap<V> is an interface so can't extend AbstractRichIterable<V>.

[kedar-joshi]

I wanted to take this up but not sure if it's still valid requirement.

[motlin]

It's still valid! The conflicts are real bugs that should be fixed. You're right about interfaces that can't extend a class.