TrigTRTHTHCounter: fix dPhi vs |dPhi| bug

Hello,

This MR is hopefully fixing a bug in TrigTRTHTHCounter that should explain why the HIP HLT chain is never firing (ATR-25537). In the past, a custom deltaPhi calculation was used (https://gitlab.cern.ch/atlas/athena/-/blob/48ee58cb73968b72b3c5d928764555dad12b1901/Trigger/TrigAlgorithms/TrigTRTHighTHitCounter/src/TrigTRTHTHCounter.cxx#L35-39), which was spanning values within [0,phi] (provided the phi1 and phi2 inputs were within [-pi,pi]...). While migrating code, this was replaced with CxxUtils::deltaPhi that is spanning values within [-pi,pi] (https://gitlab.cern.ch/atlas/athena/-/blob/23.0/Control/CxxUtils/CxxUtils/phihelper.h). With the std::abs fix, fHT_wedge can now exceed the HLT threshold of 0.4, and the chain fires.

Tagging @wtaylor , @dbakshig , @sidoti .

Cheers, Bertrand