Consider all projects in hierarchy for issue rebalance

When rebalancing issues based on a issue from a project, we need
to consider all issues in the hierarchy vs just issues in the
project's parent group and descendants, as it may happen that the
project's group is not the root group, thus not rebalancing issues
throughout the hierarchy.

app/models/issue.rb

@@ -88,7 +88,6 @@ class Issue < ApplicationRecord
     test_case: 2 ## EE-only
   }
 
-  alias_attribute :parent_ids, :project_id
   alias_method :issuing_parent, :project
 
   alias_attribute :external_author, :service_desk_reply_to
@@ -191,7 +190,8 @@ class Issue < ApplicationRecord
   end
 
   def self.relative_positioning_query_base(issue)
-    in_projects(issue.parent_ids)
+    projects = issue.project.group&.root_ancestor&.all_projects || issue.project
+    in_projects(projects)
   end
 
   def self.relative_positioning_parent_column

ee/app/models/ee/issue.rb

@@ -175,21 +175,6 @@ module EE
         user.can?(:admin_issue, project) && user.can?(:create_epic, group)
     end
 
-    # Issue position on boards list should be relative to all group projects
-    def parent_ids
-      return super unless has_group_boards?
-
-      board_group.all_projects.select(:id)
-    end
-
-    def has_group_boards?
-      board_group && board_group.boards.any?
-    end
-
-    def board_group
-      @group ||= project.group
-    end
-
     def promoted?
       !!promoted_to_epic_id
     end

ee/spec/models/issue_spec.rb

@@ -529,9 +529,10 @@ RSpec.describe Issue do
 
   describe 'relative positioning with group boards' do
     let_it_be(:group) { create(:group) }
+    let_it_be(:subgroup) { create(:group, parent: group) }
     let_it_be(:board) { create(:board, group: group) }
-    let_it_be(:project) { create(:project, namespace: group) }
-    let_it_be(:project1) { create(:project, namespace: group) }
+    let_it_be(:project) { create(:project, group: subgroup) }
+    let_it_be(:project1) { create(:project, group: group) }
     let_it_be_with_reload(:issue) { create(:issue, project: project) }
     let_it_be_with_reload(:issue1) { create(:issue, project: project1, relative_position: issue.relative_position + RelativePositioning::IDEAL_DISTANCE) }
     let(:new_issue) { build(:issue, project: project1, relative_position: nil) }