Have SCT_Digitization classes inherit from Interfaces in SiDigitization
Following discussions with @jchapman and @csebasti, move Interface class headers out of SCT_Digitization and into SiDigitization (and make them more generic), and update the implementations of these classes to inherit from them.
This will allow:
- The same Interfaces to be used outside of SCT_Digitization in dedicated Digitization packages for e.g. ITkStrip and HGTD, to be added in future MRs.
- The same implementations of e.g. SCT_FrontEnd to be used in such new packages (and new DigitizationTools), until they likely get their own dedicated class implementaions in future (once updates mean that they would need to diverge from the SCT implementation) also inheriting from the Interfaces in SiDigitization.
The motivation is to give the necessary flexibility for dedicated tools for new detectors to be added in future, while avoiding code duplication in the meantime.
NB, SCT_InducedChargeModel is also moved to SiDigitization (as InducedChargeModel) for similar reason, but in future should possibly be re-written as a ConditionsStore object.