Port of SoftKiller functionality from 21.3 to master
Part of effective TrigHLTJetRec pseudomerge.
This enables constituent pileup modifications (Voronoi subtraction + SoftKiller) to be run in the legacy jet trigger reconstruction. This depends on a helper function in JetConstitModSequence that should be removed when we move fully to the AthenaMT classes.
@peter, I changed the NegativeEnergyRejectionTool into a NonPositiveEnergyRejectionTool, to be able to reject 0 energy clusters. Steven previously set this up as a PositiveEnergySelector.
Incidentally includes a fix for memory leak in jet trimming.
Partially addresses ATR-19010.