Handle ganged segmentations.

[scott-snyder]

Some segmentations can gang together regions from multiple volumes (such as the Allegro ECal). In the calorimeter implementations of Geant4SensitiveAction, we were finding the hit position by first getting the local position from the segmentation, then converting to a global position using the transform obtained from the step. But if multiple volumes are ganged, this may not be correct: the volume which actually contains the hit may not be the same one which the segmentation used for its local coordinate system. In this case, we need to instead find the volID to use from the segmentation and get the transformation by looking it up in the volume manager.

However, not all segmentations properly implement the volumeID method needed for this, so this has to be opt-in. We add an isGanged() method to the Segmentation interface. If this is overridden with a method that returns true, then we proceed as described above. Otherwise, we preserve the present behavior.

Also factor out some duplicated code among the calorimeter implementations.

BEGINRELEASENOTES

• DD4hep::Segmentations: add cellsSpanVolumes function to mark segmentations that that can have cells that span multiple volumes, such as the Allegro ECal.

ENDRELEASENOTES

[github-actions]

Test Results

   14 files     14 suites   5h 26m 37s ⏱️
  369 tests   366 ✅ 0 💤 3 ❌
2 538 runs  2 529 ✅ 0 💤 9 ❌

For more details on these failures, see this check.

Results for commit 1b07e29.

♻️ This comment has been updated with latest results.

[andresailer]

I think "gang" sounds too much like slang (pun intended) to be clearly understood

[scott-snyder]

Thanks. I agree the naming's not great, but (as is often the case), it's
difficult to find something that's descriptive but not unwieldy.

What we're trying to get at here is, does the segmentation have cells
which can encompass multiple volumes; that is, can points from distinct
volumes be assigned to the same cell?

Some other possibilities might be:

bool cellsSpanVolumes()
bool canCellsSpanVolumes()
bool isMultiVolume()
bool multipleVolumesPerCell()

Do any of those sound ok to you?