Draft: HLT_mu3vtx_L12MU8F Trigger Updates

Updates to HLT_mu3vtx_L12MU8F trigger include changing file/directory names to be compliant with AthenaMT naming conventions; removal of intermediate variables in the TrigLongLivedParticles TrigAlgorithms package configuration files; moving all files associated with the MuonCluster class, MuonClusterHypoAlg class, and MuonClusterHypoTool class into their respective package src/ directories to match directory structure of other HLT triggers; moving/changing the include statements of these same files to be compliant with both Atlas Style Guidelines and the new package directory structure; and changes from C-ctyle casts to C++-style static casts for all float/double variables in the MuonCluster algorithm.