Add RNGWrapper::setSeedLegacy methods to support setting the random number seeds the old way

These changes make it possible to reproduce the random number seeding from the old-style AtDSFMTGenSvc random number service within the RNGWrapper for q221. In this merge request LArPileUpTool and LArTTL1Maker have been adapted to use the old approach to setting the seeds. Unclear whether anything else needs to be switched over.

This merge request also includes a small patch to TRT_Digitization configuration to ensure consistency between CA-based configuration and old-style configuration. Required after the setting of ConfigFlags.Digitization.RandomSeedOffset was altered slightly to match how offsets to random number seeds are applied in 21.0.

FYI @wlampl, @tadej, @mduehrss, @zmarshal