Fix z0 calculation in emerging jets trigger

The z0 calculation in TrigJetEJsHypoTool did not take into account the beamspot z position which led to large rates for periods with significant beamspot shifts (see ATR-27603). The implementation now aligns with the recommended way to compute z0 (see https://twiki.cern.ch/twiki/bin/view/AtlasProtected/TrackingCPRecsRun2Final#Calculating_z0_and_d0_significan)

This will lead to rate changes. I am not sure the exact protocol for updating active chains so please let me know if there are additional approvals or discussions needed.

Tagging @cpollard, @jmasik, @strom, @dguest, @ggustavi, @mgenest