Fix errant rules for associating projects when dragging tasks within a milestone column

Summary:
Fixes T10912. When you drag tasks within a milestone, we currently apply an overbroad, API-focused rule and add the parent board's project. This logic was added fairly recently, as part of T6027, to improve the behavior of API-originated moves.

Later on, this causes the task to toggle in and out of the parent project on every alternate drag.

This logic is also partially duplicated in the `MoveController`.

  - Add test coverage for this interaction.
  - Fix the logic so it accounts for subproject / milestone columns correctly.
  - Put all of the logic into the TransactionEditor, so the API gets the exact same rules.

Test Plan:
  - Added a failing test and made it pass.
  - Dragged tasks around within a milestone column:
    - Before patch: they got bogus project swaps on every other move.
    - After patch: projects didn't change (correct).
  - Dragged tasks around between normal and milestone columns.
    - Before patch: worked properly.
    - After patch: still works properly.

Here's what the bad changes look like, the task is swapping projects with every other move:

{F1255957}

The "every other" is because the logic was trying to do this:

  - Add both the parent and milestone project.
  - Whichever one exists already gets dropped from the change list because it would have no effect.
  - The other one then applies.
  - In applying, it forces removal of the first one.
  - Then this process repeats in the other direction the next time through.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10912

Differential Revision: https://secure.phabricator.com/D15834

src/applications/project/controller/PhabricatorProjectMoveController.php

@@ -96,32 +96,6 @@ final class PhabricatorProjectMoveController
       }
     }
 
-    $proxy = $column->getProxy();
-    if ($proxy) {
-      // We're moving the task into a subproject or milestone column, so add
-      // the subproject or milestone.
-      $add_projects = array($proxy->getPHID());
-    } else if ($project->getHasSubprojects() || $project->getHasMilestones()) {
-      // We're moving the task into the "Backlog" column on the parent project,
-      // so add the parent explicitly. This gets rid of any subproject or
-      // milestone tags.
-      $add_projects = array($project->getPHID());
-    } else {
-      $add_projects = array();
-    }
-
-    if ($add_projects) {
-      $project_type = PhabricatorProjectObjectHasProjectEdgeType::EDGECONST;
-
-      $xactions[] = id(new ManiphestTransaction())
-        ->setTransactionType(PhabricatorTransactions::TYPE_EDGE)
-        ->setMetadataValue('edge:type', $project_type)
-        ->setNewValue(
-          array(
-            '+' => array_fuse($add_projects),
-          ));
-    }
-
     $editor = id(new ManiphestTransactionEditor())
       ->setActor($viewer)
       ->setContinueOnMissingFields(true)