Gets rid of a compile-time cycle and shrinks many others: https://www.diffchecker.com/n1Sru9kA
ChatMessageValidator has a compile-time dep on SafeText (not much we can do about that).
SafeText depends on Pleroma.HTML which depends on Activity, creating compile-time cycles.
The solution is to keep Pleroma.HTML very simple and break out activity-related functions into a separate module, Pleroma.Activity.HTML.