Splitting the InDetReadoutGeometry into different technologies as done in 21.9, as a prelude to cleaning up code and integrating ITK functionality. This is step 1. At this stage a number of classes will be (temporarily) duplicated between InDetReadoutGeometry and Pixel/SCT_/TRT_ReadoutGeometry.
Incremental Merge Requests will follow where client classes are updated to use the versions of Pixel/SCT/TRT-specific classes from these new classes rather than from InDetReadoutGeometry in step 2.
In step 3, the duplicate Pixel/SCT/TRT-specific classes will be removed from InDetReadoutGeometry.