Mark PhabricatorPHIDType::getPHIDTypeApplicationClass() as abstract

Summary: Fixes T9625. As explained in a `TODO` comment, seems reasonable enough.

Test Plan: Unit tests.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, hach-que

Maniphest Tasks: T9625

Differential Revision: https://secure.phabricator.com/D14068

src/applications/spaces/phid/PhabricatorSpacesNamespacePHIDType.php

@@ -9,14 +9,14 @@ final class PhabricatorSpacesNamespacePHIDType
     return pht('Space');
   }
 
-  public function getPHIDTypeApplicationClass() {
-    return 'PhabricatorSpacesApplication';
-  }
-
   public function newObject() {
     return new PhabricatorSpacesNamespace();
   }
 
+  public function getPHIDTypeApplicationClass() {
+    return 'PhabricatorSpacesApplication';
+  }
+
   protected function buildQueryForObjects(
     PhabricatorObjectQuery $query,
     array $phids) {