[FEA] Revisit GpuTextBasedPartitionReader and how returned values are cast to the final result

[revans2]

Is your feature request related to a problem? Please describe.
GpuTextBasedPartitionReader was written without any nested types support at all. We are starting to add this in for JSON, but JSON is getting to be a little tricky because we might end up with needing to recursively call parse some columns that are returned. Also the JSON, CSV, and HiveText formats do not really share all that much in terms of parsing once we get into the details of it. Once we have a better understanding of how the final JSON code will work we should come back and revisit this so that the design is cleaner.