Consolidate transaction generation in EditType objects
Summary:
Ref T9132. This is a bit more cleanup to make adding CustomField support easier.
Right now, both `EditField` and `EditType` can actually generate a transaction. This doesn't matter too much in practice today, but gets a little more complicated a couple of diffs from now with CustomField stuff.
Instead, always use `EditType` to generate the transaction. In the future, this should give us less total code and make more things work cleanly by default.
Test Plan: Used web UI and Conduit to make various edits to pastes, including doing race-condition tests on "Projects".
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T9132
Differential Revision: https://secure.phabricator.com/D14607