First-Class Array Abstractions

[tustvold]

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

Currently Array are wrappers around an ArrayData, storing it as a member of the array. This is redundant, confusing and results in API friction.

Describe the solution you'd like

I would like the Array implementations to just store their constituent parts, in the same vein as the typed ArrayData abstractions experimented with under #1799 did. This would involve the following

• Add Array::nulls(&self) -> Option<&NullBuffer>
• Add Array::to_data(&self) -> ArrayData
• Implement Array::slice, Array::data_type, Array::len, Array::get_buffer_memory_size, etc... for each Array
• Deprecate Array::data, Array::data_ref and Array::offset

Describe alternatives you've considered

Additional context

#3879