Make FixedSizeBinaryArray value_data return a reference

[wjones127]

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

Right now, you cannot get a reference the the value data in a FixedSizeBinaryArray. You can get a clone of the buffer from value_data.

Describe the solution you'd like

Instead of returning a clone of the buffer, just return a reference. The caller can clone the reference if they want.

Describe alternatives you've considered

Additional context