xAODTrig: Enable thread-safety checker and related fixes
Enable the thread-safety checker for most of the xAODTrig* packages and
apply the relevant fixes (mostly just static -> static const). The
following packages require less trivial fixes and still need to be done:
xAODTrigRingerAthenaPool
xAODTrigBphysAthenaPool
xAODTrigMuonAthenaPool
xAODTrigCaloAthenaPool
xAODTrigEgammaAthenaPool
xAODTriggerAthenaPool
xAODTrigger