Dynamic form pages

Options, more or less in order of my personal preference

1. Comprehensive dynamic vue code that gets generated in one place. We only have to define which questions are reliant on which answers once. This could either be in the Backend or Frontend. This would require the most work but would be the best option in the long run.
2. A better version of Check-requires which updates visible fields based on a response from the backend. This allows us to write all logic in the backend, and still have a nice frontend (with Vue?).
3. Hard-coded JS in the templates with backend validation. Less desirable because it's hard to maintain and prone to breakage.
4. Do everything in the backend, like with the Grant Tool. Every question reliant on a previous field requires a page load.

No files, tests, or entry points are named. Start by inspecting the existing Check-requires behavior and the Grant Tool's backend-only approach, then compare them with the four proposed designs. Done requires a chosen approach for dependent form fields, with backend validation and behavior that updates or reloads fields according to earlier answers.

Written by the indexing model from the issue text.