## Description
tl;dr Fixed APCA contrast checks for both light and dark modes (detailed
info in the ticket). Refined how we pick shade or tint for `fgOnAccent`.
Fixes#23218
## Type of change
- Bug fix (non-breaking change which fixes an issue)
- Chore (housekeeping or task changes that don't impact user perception)
## How Has This Been Tested?
- Manual
### Test Plan
Initial POC refinement, no testing necessary
## Checklist:
### Dev activity
- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] PR is being merged under a feature flag
### QA activity:
- [ ] Test plan has been approved by relevant developers
- [ ] Test plan has been peer reviewed by QA
- [ ] Cypress test cases have been added and approved by either SDET or
manual QA
- [ ] Organized project review call with relevant stakeholders after
Round 1/2 of QA
- [ ] Added Test Plan Approved label after reveiwing all Cypress test