Unbreak the creation of Packages Versions

Summary:
Allow the creation of versions in Packages
by specifying a dummy Package to allow the
extended policy checks to pass. Versions
require that the package they're a version
of be accessible to the viewer, but that
means a package is required during creation.

This also initializes the attached package
property to the un-attached state, which
was missing. This should make it easier to
fix when misused.

Currently trying to create versions in Packages throws:
```
EXCEPTION: (Error) Call to a member function getPHID() on null at [<phorge>/src/applications/policy/filter/PhabricatorPolicyFilter.php:404]
```

Test Plan:
* Visit /applications/view/PhabricatorPackagesApplication/ and enable the Packages prototype application
* Visit /packages/version/edit/form/default
* Observe an edit form instead of an exception

Reviewers: O1 Blessed Committers, aklapper

Reviewed By: O1 Blessed Committers, aklapper

Subscribers: aklapper, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Differential Revision: https://we.phorge.it/D25882

src/applications/packages/editor/PhabricatorPackagesVersionEditEngine.php

@@ -19,7 +19,11 @@ final class PhabricatorPackagesVersionEditEngine
 
   protected function newEditableObject() {
     $viewer = $this->getViewer();
-    return PhabricatorPackagesVersion::initializeNewVersion($viewer);
+    return PhabricatorPackagesVersion::initializeNewVersion($viewer)
+      // Attach a dummy package to have the policy checks pass for this object
+      // during creation.
+      ->attachPackage(
+        PhabricatorPackagesPackage::initializeNewPackage($viewer));
   }
 
   protected function newObjectQuery() {

src/applications/packages/storage/PhabricatorPackagesVersion.php

@@ -15,7 +15,7 @@ final class PhabricatorPackagesVersion
   protected $name;
   protected $packagePHID;
 
-  private $package;
+  private $package = self::ATTACHABLE;
 
   public static function initializeNewVersion(PhabricatorUser $actor) {
     return id(new self());