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.

@ckaldero, @jroloff FYI. @cantel, hopefully this doesn't conflict with !21649 (merged).

Partially addresses ATR-19010.