Refactor PhlSeniorCitizenTaxFreeze to use new checks

[prestoncabe]

This wires up the following checks to the SCTF library benefit:

• OwnerOccupant
• LivesInPhiladelphiaPa

The remaining eligibility check for this is a complex age requirement. It is implemented in the SCTF library benefit DMN. I intend to implement it as a custom check as part of #339 .

The complex age requirement raised some interesting questions about how to implement similar checks in the future. We will likely eventually need to have better solutions for:

• How might we share data facts between library and custom checks?
  • We discussed possibly using the same "situation" input across library and custom checks.
  • We also discussed finding a way to use the same data shape for all three of: custom checks/form editor/library checks
  • Another related feature that will help: supporting library benefits in the web app. This is another route to allowing users to bypass complex/bespoke benefit logic.
• How might we access library checks from within custom checks?
  • There are a few different approaches from backend and UX standpoint we could take with this
  • This is probably blocked until we figure out the data sharing question

I'm punting/letting go of the above questions for now because of two recent realizations:

• In the set of 5 property tax relief benefits, there are no age-related requirements except for SCTF. So, we don't need to solve the data-sharing question right now.
• There is a simple enough workaround to sharing data between custom and library checks that I wasn't considering before: mapping data in the form editor using the Expression Component (e.g. setting custom.clientDateOfBirth to people.client.dateOfBirth). Ideal? No. But simple enough that I think it buys us time to finish the Prototype v2 milestone, get this in front of users, and prioritize a long-term solution based on their feedback.

[prestoncabe]

@Justin-MacIntosh @Michael-Dratch See my notes above for my latest thinking on the question of data sharing between custom checks and library checks.