Show crosshair gap

Summary:
Reuse the existing plane geometry data

This will correctly render the crossing lines of the planes.
Without this the PlaneGeometryDataMapper2D::CreateVtkCrosshair will not
find other planes for computing the intersection point correctly.

Test Plan:
manual testing

1. open MITK, close the StdDisplay, open the mxnDisplay
2. load an image and set the crosshair to a different position
3. see how the crosshair gap is visible on both lines of the crosshair

Reviewers: s434n, O1 MITK Reviewer Group I

Reviewed By: s434n, O1 MITK Reviewer Group I

Subscribers: kalali, s434n

Maniphest Tasks: T29383

Differential Revision: https://phabricator.mitk.org/D755