[FEA] Review JsonToStruct and JsonScan and consolidate some testing and implementation

[andygrove]

Is your feature request related to a problem? Please describe.
PR #9666 adds support for parsing dates from JSON specifically for GpuJsonToStructs and there are differences in how we handle parsing dates compared to GpuJsonScan.

Describe the solution you'd like
There are opportunities to make the code more consistent between the two approaches of parsing JSON and ensure that tests are consistent and have more coverage.

Describe alternatives you've considered

Additional context

[andygrove]

This is related to #4940 as well

[revans2]

I think this was mostly done by #10542

But the testing is being done by #10491 and #10492

There are also a lot of follow on fixes that need to be done.