Refactor the Kiddie Tax logic and separate it from AMT

Currently we have made small adjustments in #5086 to eliminate the AMT application to young head of households, but we should separate the logic out fully as we do not account for multiple calculations:
- We need to apply the AMT to unearned income specifically
- We should separate the kiddie tax calculation entirely
- We dont account for young / student dependents - just account for households with young heads / spouses

Potentially other limitations

We should have separate files for the kiddie tax calculation as well as applicable income for the kiddie tax