Expose linked work item state on LinkedItemType

What does this MR do and why?

Resolves #481590 (closed)

Exposes the state of a linked item to a work item via it's linked items widget, rather than forcing the client to go into the workItem and get that value specifically, saving one level of nesting from the query.

Before:

query {
  workItem(id:"gid://gitlab/WorkItem/642") {
    id
    title
    widgets {
      ... on WorkItemWidgetLinkedItems {
        linkedItems {
          nodes {
            workItem {
              title
              state
            }
          }
        }
      }
    }
  }
}

After:

query {
  workItem(id:"gid://gitlab/WorkItem/642") {
    id
    title
    widgets {
      ... on WorkItemWidgetLinkedItems {
        linkedItems {
          nodes {
            workItemState
          }
        }
      }
    }
  }
}

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Before	After

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