Move afform to be a core extension
The goal with afform has always been to use it to eventually migrate off our old unweildly forms & replace them with afforms over time. We identified moving it to be a core extension as a goal for next week. this basically involves
- copying the code to the ext dir & committing it
- updating the existing repo as discontinued
- wiring up tests & enabling on install on new buildkit installs.
Further steps to ensure it's enabled on upgrade or on new installs don't need to be in scope at this stage