Fix a complicated object caching issue with the policy filter

Summary:
Fixes T11853. To set this up:

• Create "Project A".
• Join "Project A".
• Create a subproject, "Project A Subproject 1".
  • This causes Project A to become a parent project.
  • This moves you to be a member of "Project A Subproject 1" instead of "Project A" directly.
• Create another subproject, "Project A Subproject 2".
  • Do not join this subproject.
• Set the second subproject's policy to "Visible To: Members of Project A".
• Try to edit the second subproject.

Before this change, this fails:

• When querying projects, we sometime try to skip loading the viewer's membership in ancestor projects as a small optimization.
• Via PhabricatorExtendedPolicyInterface, we may then return the parent project to the policy filter for extended checks.
• The PolicyFilter has an optimization: if we're checking an object, and we already have that object, we can just use the object we already have. This is common and useful.
• However, in this case it causes us to reuse an incomplete object (an object without proper membership information). We fail a policy check which we should pass.

Instead, don't skip loading the viewer's membership in ancestor projects.

Test Plan:

• Did all that stuff above.
• Could edit the subproject.
• Ran arc unit --everything.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11853

Differential Revision: https://secure.phabricator.com/D16840