Add split-sensor functionality to StripDigitization
This adds functionality needed to process "split sensors" (plus a few updates to how dictionaries are handled for local geometries) in the ITk-specific strip digi package.
This digitization package is not the default used; it can be activated with
from Digitization.DigitizationFlags import digitizationFlags; digitizationFlags.experimentalDigi+=["doStripDigi"]