HLT_mu3vtx_L12MU8F Trigger Improvements

Renamed package TrigL2LongLivedParticles to TrigLongLivedParticles and made additional changes to remove L2 from filenames in this package and the associated Hypothesis package, TrigLongLivedParticlesHypo.

Minor issues being fixed include violations of the ATLAS style guide & best coding practices, such as using the c++ dynamic_cast and static_cast functions instead of C-style casts; removal of duplicate "include" statements; and others. Changed hard-coded pi in TrigLongLivedParticlesMonitoring.py to math.pi.

All header and source files have been moved into their respective package src/ directories to match the directory structure present in other triggers. Intermediate variables in the the python configuration files have been removed. MuonClusterHypoAlg methods "initialize" and "execute" were changed to virtual, override methods. The SG Key for the TrigCompositeContainer that stores the muon RoI clusters has been updated to "HLT_RoICluster_Container" in preparation to be added to the Run3 EDM configuration so these objects get written to the output file, !54628 (closed).