Measure entered pre-2022 combined sales tax rates against that year's state rate #9914

Problem

Worksheet line 3, local_sales_tax_rate, is the combined rate less the state's general sales tax rate:

• in the official-rate states, that rate comes from policyengine_us/data/local_sales_tax/state_rates.csv (added in Model the IRS local sales tax worksheet with official locality rates #9879);
• elsewhere it is the state table heading (state_sales_tax_table/rate.yaml).

The state rate file starts on 2022-01-01, and its first row also covers earlier years. So when a user enters a combined rate for a year before 2022, line 3 subtracts the 2022 state rate, not that year's. The IRS's line 3 is that year's local rate. The two differ in three states:

In every other official-rate state, the 2015-2021 headings equal the 2022 official rates. #9911 adds the year-specific headings.

Example. Kansas 2015 with a 7.5% combined rate entered: line 3 should be 1.1736 (7.5 − 6.3264). PolicyEngine gives 1.0 (7.5 − 6.5).

Constraint

With no rate entered, the pre-2022 combined rate is the key's 2022 official rate. Subtracting the 2022 state rate gives the 2022 local rate, which is coherent. Simply using the heading before 2022 would invent local tax in county areas that have none, for example 0.5 points in South Dakota 2015. #9911's YAML cases for Beadle County SD and Butler County KS in 2015 hold that at 0.

Possible fix

• In local_sales_tax_rate, use the official state rate only from the state file's first date, and the heading before it.
• In combined_sales_tax_rate, for years before the locality files begin, return the 2022 official combined rate less the 2022 official state rate plus that year's heading.

With both changes, the default line 3 stays the 2022 local rate, an entered combined rate is measured against the year's heading, and 2022+ results are unchanged. This is a methodology choice, so it needs a reviewer's judgment.

Depends on #9879 and #9911.