(graphics): add slices lines on SNegato2D
Description
Add lines in 2D negatoscopes showing the positions of slices perpendicular to the current plane.
Functional specifications
- Show a blue, red, green line for axial, sagittal and frontal planes.
Technical specifications
Modify module::viz::scene3d::SNegato2D
/viz::scene3d::Plane
accordingly, using the image fields.
Test plan
Probably not needed to change test data since the metrics are a bit permissive, manual testing might be enough.