(viz): add intensity picking in 2D negatoscope
Description
It is currently possible to pick intensities in 3D negatoscopes, but not in 2D negatoscopes. It would be really useful.
Functional specifications
We want exactly the same behavior as the 3D negatoscope.
Technical specifications
This should be a copy & paste, but maybe there is some room for code sharing.
Test plan
Manual testing only, maybe automated testing if the MR makes its way before.