[FEA] simplify page_state_s and possibly other structures for specialized parquet kernels

[abellina]

@vuule brought up the point here #15159 (comment) that page_state_s could be simplified for the fixed/fixed dictionary kernels, as they don't need all the members of this structure and it might help with shared memory use.

I also think there are other shared structures that we should audit and clean up. I am filing this issue so we don't loose track of it.