Adding functionality for selection on strip hit pair dPhi (between stereo-layers), making use of existing SiSpacePointMakerTool. Principally for upgrade tracking with ITK, hence 21.9, but interested in trying for run-3 hence also targeting master.
Contrary to branch name, this has had 21.9.13 merged in and is tested in that release.
WIP as needs configuration tidying up, and maybe should move to own tool. Making MR as it's easier to keep track of changes wrt 21.9 like this. Supersedes earlier MR on dev branch (!35604 (closed))