GraphQL Integration

Integration added.
Before the integration one could execute the referenced view like this:

query ViewsReferenceFieldDemo {
  entityById(entityType: PARAGRAPH, id: 110) {
    ... on ParagraphViewsReferenceFieldDemo {
      bpViewRawField {
        first {
          entity {
            executable(displayId: "block_1") {
              execute {
                rows {
                  __typename
                  id
                  label
                }
              }
            }
          }
        }
      }
    }
  }
}

The change keeps this behavior untouched - but you can now use the following query to execute the view with viewsreference pre-configured:

query ViewsReferenceFieldDemo {
  entityById(entityType: PARAGRAPH, id: 110) {
    ... on ParagraphViewsReferenceFieldDemo {
      bpViewRawField {
        first {
          executable {
            execute {
              rows {
                __typename
                id
                label
              }
            }
          }
        }
      }
    }
  }
}

I had to duplicate quite a bit of code from \Drupal\viewsreference\Plugin\Field\FieldFormatter\ViewsReferenceFieldFormatter::viewElements().
I think it's worth considering outsouring the preparation / building of the view into maybe a trait.