Add TypedDictionaryArray for more ergonomic interaction with DictionaryArray

[tustvold]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

DictionaryArray does not know the type of its underlying child array, and therefore cannot implement ArrayAccessor directly.

Describe the solution you'd like

Introduce something like the following

pub struct TypedDictionaryArray<'a, K: ArrowDictionaryKeyType, T: ArrayAccessor> {
    dict: &'a DictionaryArray<K>,
    values: T
}

impl <'a, K: ArrowDictionaryKeyType, T: ArrayAccessor> ArrayAccessor for TypedDictionaryArray<'a, K, T> {
    ...
}

This will allow having standard implementations of kernels in terms of ArrayAccessor that will also work for DictionaryArray (once downcast to the appropriate type).

Describe alternatives you've considered
We could continue to special case the various different types of dictionary, using macros to reduce duplication

Additional context

#2135