ArrayData.align_buffers should support Struct data type / child data

[EnricoMi]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Method ArrayData.align_buffers ensures that data in the array buffers are aligned. This is needed if data come from IPC or FFI. In case of DataType::Struct, mis-aligned buffers are currently not aligned by this method, because it only aligns self.buffers, not buffers of self.child_data.

Describe the solution you'd like
Make ArrayData.align_buffers align buffers of child data recursively.

[alamb]

label_issue.py automatically added labels {'arrow'} from #6462