Split out reported state income tax between refundable credits and state tax before refundable credits

We need this to ensure that tax before refundable credits are nonnegative under both baseline law and the reform to use reported state tax. So we should use `STATETAX_B` for that ([source](https://www2.census.gov/programs-surveys/cps/datasets/2022/march/asec2022_ddl_pub_full.pdf#page=52)).