R1:83c0fda28059

Modularize all remaining Maniphest Herald fields

Summary:
Ref T8726. The only notable bit here is that the "body" / "title" fields (which are currently shared across a bunch of types) are getting split into application variants.

Among other things, this will let us label the field "Commit message" for commits, for example.

Test Plan:
- Created a rule using all four fields.
- Applied patch, saw rule break ("unknown field").
- Ran storage upgrade, saw rule fix itself in the migration.
- Edited…