Align usages of Project#marked_for_deletion? to account for ancestors

Background

Follow-up from #457718 (comment 2174193752).

In Marking a group as 'pending deletion' should ma... (#457718 - closed) we changed projects to be pending deletion if the parent group is also pending deletion. There are a number of places we are still using Project#marked_for_deletion? but that method doesn't account for the parent group being pending deletion.

Proposal

Maybe we should rename self_or_ancestor_marked_for_deletion into pending_delete? or something like that?

We then have:

• marked_for_deletion? (true if user marked the group or project for deletion)
• pending_deletion? (true if the group or project will be deleted because a parent group is marked_for_deletion)
• marked_for_deletion_on should return a date for ancestor groups and projects when parent is marked for deletion. Currently it returns nil.

Implementation guide

Needs refinement