Support object mentions in Calendar Event descriptions

Summary:
Ref T7924. This:

  - Adds support for remarkup block changes to Modular Transactions.
  - Exposes remarkup changes from the Calendar event "Description" transaction.

This makes stuff like mentions and file embeds work properly.

Test Plan:
Mentioned a task in an event description, saw a mention appear on the task.

Uploaded a file to an event description, saw the file become "Attached" to the event.

(Neither of these worked properly before.)

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T7924

Differential Revision: https://secure.phabricator.com/D16481

src/applications/calendar/xaction/PhabricatorCalendarEventDescriptionTransaction.php

@@ -39,4 +39,15 @@ final class PhabricatorCalendarEventDescriptionTransaction
       ->setNewText($this->getNewValue());
   }
 
+  public function newRemarkupChanges() {
+    $changes = array();
+
+    $changes[] = $this->newRemarkupChange()
+      ->setOldValue($this->getOldValue())
+      ->setNewValue($this->getNewValue());
+
+    return $changes;
+  }
+
+
 }

src/applications/transactions/storage/PhabricatorModularTransaction.php

@@ -149,4 +149,8 @@ abstract class PhabricatorModularTransaction
     return parent::renderChangeDetails($viewer);
   }
 
+  final protected function newRemarkupChanges() {
+    return $this->getTransactionImplementation()->newRemarkupChanges();
+  }
+
 }

src/applications/transactions/storage/PhabricatorModularTransactionType.php

@@ -67,6 +67,10 @@ abstract class PhabricatorModularTransactionType
     throw new PhutilMethodNotImplementedException();
   }
 
+  public function newRemarkupChanges() {
+    return array();
+  }
+
   final public function setStorage(
     PhabricatorApplicationTransaction $xaction) {
     $this->storage = $xaction;
@@ -253,4 +257,9 @@ abstract class PhabricatorModularTransactionType
     return ($target == PhabricatorApplicationTransaction::TARGET_TEXT);
   }
 
+  final protected function newRemarkupChange() {
+    return id(new PhabricatorTransactionRemarkupChange())
+      ->setTransaction($this->getStorage());
+  }
+
 }