[FEA] Support nested structs for pivot first

[revans2]

Is your feature request related to a problem? Please describe.
pivot first is a combination of GpuIf, GpuEqualTo, literal values, and nth in cudf. Many of these things do not work for nested structs yet. But once they do we should be able to support PivotFirst

• copy_if_else should be fully working
• GpuEqualTo requires [FEA] Add nested struct support for comparison operations rapidsai/cudf#8964
• nth/GpuLast requires [FEA] add nested struct support for nth reduction and group by aggregation rapidsai/cudf#8967
• Literal values should be fully working for just structs, but there have been a few issues with lists

After that we need to update the type checking and add some more tests.