readout geometry splitting for SCT and TRT

Continuing the work from !29949 (merged)

So far, CMakeLists are updated "additively" so there may be some places where we still have InDetReadoutGeometry listed as a dependency where it is not strictly needed. If its OK I'd like to remove these cases in a final clean-up step in a new MR, once the switch over is seen to work and the changes here are merged.