Add block counts to linked items widget

Related to #416768 (closed)

What does this MR do and why?

This is the following iteration for !126980 (merged) where we added a GraphQL query to expose the items linked to a work item.

Similarly to IssueType, we also want to expose the field blocked, blockedByCount and blockingCount for a work item so these can now be included in the WorkItemWidgetLinkedItems widget added in !126980 (merged).

Summary of changes

• Extend LinkedItemsType to add the EE scoped fields blocked, blocking_count and blocked_by_count
• Add a new LazyLinksAggregate file for work item links. This aggregator is used for blocked and blocked_by_count fields
• Move EE::IssueLink logic to LinkableItem concern so it can be shared with WorkItems::RelatedWorkItemLink. This functionality will refresh the blocking count for a work item when a link is created or destroyed (used by blocking_count field).

I have also included notes inline to explain more specific changes

❗ This feature remains behind the feature flag :linked_work_items

Screenshots or screen recordings

❗ This MR doesn't introduce any UI changes

example query

How to set up and validate locally

1. Using rails console enable the feature flag

Feature.enable(:linked_work_items)

2. Create the work items and links

author, project = User.first, Project.first
wi_type = WorkItems::Type.find_by(base_type: 'task')
task = WorkItem.create!(title: "Source Task", project: project, author: author, work_item_type: wi_type)

blocked_task = WorkItem.create!(title: "Blocked Task", project: project, author: author, work_item_type: wi_type)
blocking_task1 = WorkItem.create!(title: "Blocking Task 1", project: project, author: author, work_item_type: wi_type)
blocking_task2 = WorkItem.create!(title: "Blocking Task 2", project: project, author: author, work_item_type: wi_type)

WorkItems::RelatedWorkItemLink.create!(source: task, target: blocked_task, link_type: 'blocks')
WorkItems::RelatedWorkItemLink.create!(source: blocking_task1, target: task, link_type: 'blocks')
WorkItems::RelatedWorkItemLink.create!(source: blocking_task2, target: task, link_type: 'blocks')

3. Visit https://gdk.test:3000/-/graphql-explorer and verify that the following query returns the expected values

query

query getLinkedITems {
  workItem(id: "gid://gitlab/WorkItem/NOTE_ID") {
    widgets {
      ...on WorkItemWidgetLinkedItems {
        blocked
        blockingCount
        blockedByCount
        linkedItems {
          edges {
            node {
              linkType
              workItem {
                title
              }
            }
          }
        }
      }
    }
  }
}

response

{
  "data": {
    "workItem": {
      "widgets": [
        {
          "blocked": true,
          "blockingCount": 1,
          "blockedByCount": 2,
          "linkedItems": {
            "edges": [
              {
                "node": {
                  "linkType": "blocks",
                  "workItem": {
                    "title": "Blocked Task"
                  }
                }
              },
              {
                "node": {
                  "linkType": "is_blocked_by",
                  "workItem": {
                    "title": "Blocking Task 1"
                  }
                }
              },
              {
                "node": {
                  "linkType": "is_blocked_by",
                  "workItem": {
                    "title": "Blocking Task 2"
                  }
                }
              }
            ]
          }
        },
        {}
      ]
    }
  }
}

MR acceptance checklist

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