Clean up "reorder" permissions in MenuEngine for personal favorites

Summary:
Fixes T12159. This is similar to D17228, which fixed this for the main configuration operation.

Most other edit operations only test for edit capability on the MenuItem itself, which we already do correctly. However, because reordering affects all items, we test for capability on the object.

Weaken this when reordering custom items.

Test Plan: Reordered custom items in Favorites as a non-administrator.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12159

Differential Revision: https://secure.phabricator.com/D17257