Draft: Multiple scattering in dd4hep

Compute material parameters that are needed for multiple scattering corrections.

Not yet ready, for discussion

Next steps

• make a test returning the list of materials from dd4hep
• compare the spread of particles from the particle gun with what the extrapolator computes, and see what happens

@bcouturi @mveghel @dovombru @decianm

Goes with Rec!3686, related to Rec#429

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Validated by

• Core Software
• RTA
• Simulation