Create pile-up events hash and store it in xAOD::EventInfo, master edition (ATLASSIM-3795)
It might be useful to have an information how many pile-up events repeat in an analysis (e.g. we get exactly the same mixture of minbias events). This MR adds a 128-bit MD5 hash of pile-up info to the xAOD::EventInfo objects.
!20788 (merged) was updated to be compatible with master. Please review again.