(stable) Write edge transactions in a more compact way
Summary: Depends on D18946. Ref T13051. Begins writing edge transactions as just a list of changed PHIDs.
Test Plan: Added, edited, and removed projects. Reviewed transaction record and database. Saw no user-facing changes but a far more compact database representation.
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T13051
Differential Revision: https://secure.phabricator.com/D18947