R1:e8c490958c8a

Stop writing new TYPE_PROJECTS transactions to Maniphest

Summary:
Ref T5245. We'll still display the old ones, but write real edge transactions now -- not TYPE_PROJECTS transactions.

Some code remains to show the existing transactions. The next diff will modernize the old transactions so we can remove this code.

Test Plan:
- Previewed a project-editing comment.
- Submitted a project-editing comment.
- Edited a task's projects.
- Batch edited a task's projects.

Reviewers: joshuaspence, chad…