Reduce the itemized deductions in Idaho by the SALT amount

[PavelMakarchuk]

Currently we exclude salt completely,

Form

Instructions

Should pass the following test:

- name: Tax unit with taxsimid 58820 in k21.its.csv and k21.ots.csv
  absolute_error_margin: 0.01
  period: 2021
  input:
    people:
      person1:
        age: 56
        employment_income: 110010
        qualified_dividend_income: 1005.0
        taxable_interest_income: 5505.0
        short_term_capital_gains: 3505.0
        long_term_capital_gains: 1505.0
        rental_income: 1005.0
        taxable_private_pension_income: 2500.0
        real_estate_taxes: 4000
        mortgage_interest: 36000
        self_employment_income: 127010
        business_is_qualified: true
        business_is_sstb: false
        w2_wages_from_qualified_business: 100e6
        ssi: 0  # not in TAXSIM35
        state_supplement: 0  # not in TAXSIM35
        wic: 0  # not in TAXSIM35
        ma_covid_19_essential_employee_premium_pay_program: 0  # not in TAXSIM35
      person2:
        age: 56
        employment_income: 141010
        qualified_dividend_income: 1005.0
        taxable_interest_income: 5505.0
        short_term_capital_gains: 3505.0
        long_term_capital_gains: 1505.0
        rental_income: 1005.0
        taxable_private_pension_income: 2500.0
        ssi: 0  # not in TAXSIM35
        state_supplement: 0  # not in TAXSIM35
        wic: 0  # not in TAXSIM35
        ma_covid_19_essential_employee_premium_pay_program: 0  # not in TAXSIM35
    tax_units:
      tax_unit:
        members: [person1, person2]
        premium_tax_credit: 0  # not in TAXSIM35
        local_income_tax: 0  # not in TAXSIM35
        state_sales_tax: 0  # not in TAXSIM35
        ca_use_tax: 0  # not in TAXSIM35
        il_use_tax: 0  # not in TAXSIM35
        nm_2021_income_rebate: 0  # not in TAXSIM35
        nm_additional_2021_income_rebate: 0  # not in TAXSIM35
        nm_supplemental_2021_income_rebate: 0  # not in TAXSIM35
        ny_supplemental_eitc: 0  # not in TAXSIM35
        ok_use_tax: 0  # not in TAXSIM35
        pa_use_tax: 0  # not in TAXSIM35
        vt_renter_credit: 0  # not in TAXSIM35
        tax_unit_itemizes: True
        state_income_tax: 21664.05
    spm_units:
      spm_unit:
        members: [person1, person2]
        snap: 0  # not in TAXSIM35
        tanf: 0  # not in TAXSIM35
    households:
      household:
        members: [person1, person2]
        state_fips: 16  # ID
  output:  # expected results from patched TAXSIM35 2024-03-17 version
    id_income_tax: 21404.06

[MaxGhenis]

Note this isn't all SALT--doesn't include property taxes.