WIP pixel ID scheme for ITk
XML-based customization of pixel ID readout.
Fixes ATLITKSW-72.
Requires updates of XML files (ITKLayouts) describing Step3 layout(s).
Main idea : dissociate the GeoModel layout structure and the readout identification by redefining the readout layers via xml. Limitation: can only work by splitting GeoModel layer into sublayers, i.e the pixel inner endcap is defined as single GeoModel layer and the readout is customized. Gains : fixes numerous problems accompanying LTF2 developments (overflowing id ranges, hardcoded offsets, mismatched material for pixel services). Options: this import contains the redefinition of b-layer for SLHC layouts (= barrel AND edcap layer 0). Another possibility would be to redefine part of GeoModel endcap layer as readout barrel region (using the same xml customization) but this would need an update of SiNumerology class and its clients.