SiDigitization changes for use by HGTD
Since the HGTD will use common ReadoutGeometry base classes, it should also use a common base for Digitization.
This update allows for HGTD Digitization to use
SiChargedDiodeCollection etc by making them use
ReadoutGeometryBase classes rather than
Interface classes such as
ISCT_FrontEnd etc are added such that they can be used for HGTD as well. In a future MR the old interfaces will be moved out of
SCT_Digitization, and the inheritance of the derived implementations there updated to use the new abstract interfaces added here.