R1:959504a4881c

When predicting object policies for project milestones, adjust objects so they behave like milestones

Summary:
Ref T13462. Currently, when testing milestone edit policies during creation, the project object does not behave like a milestone:

- it doesn't have a milestone number yet, so it doesn't try to access the parent project; and
- the parent project isn't attached yet.

Instead: attach the parent project sooner (which "should" be harmless, although it's possible this has weird side effects); and…